fix(app): 对齐 Open Design spec — 字体/Token/首页/Tab栏/路由/Discover页

针对 docs/opendesign/warm-notes-design-spec.md 全面审查的修复：

## 🔴 阻断级修复（商用合规）
- 下载真实 Quicksand/Nunito 字体文件（原 0 字节）
- 添加 OFL.txt 许可证文件，履行 SIL Open Font License 分发义务

## 🟠 设计 Token 偏差
- AppRadius: 删除非规范的 xs=8px，所有引用迁移至 sm=10px
- AppColors.moodColors: 对齐 spec §3.6
  - happy #FFD93D → secondary #81B29A
  - calm #81B29A → tertiary #F2CC8F
  - sad #7B9CC4 → #5B7DB1
  - thinking #B8A9C9（淡紫，spec 无）→ #8B7E74
- AppShadows: blurRadius/alpha 精确对齐 spec §1 (12/20/32 + 0.06/0.08/0.12)
- DesignTokens: 补 spacing40 + 新增 safe-top/safe-bottom/tab-height/touch-min 常量

## 🟠 首页 §3.4 完全重构
- 新增问候语头部（xx好，小暖 + accent 色高亮名字）
- 新增 streak-badge pill 徽章（tertiary-soft + #B8860B 暖金）
- 心情选择器卡片背景从 primaryContainer 改为 surface（spec 规定 #FFFFFF）
- 心情卡片圆角 lg(22) → md(16) 对齐 spec
- 新增 today-card 渐变卡片 + 浮动右下圆形写按钮
- 新增 quick-stats 三栏统计（本月日记/连续天数/总日记数）
- 移除 AppBar 多余的贴纸/模板按钮，搜索按钮改路由到 /search
- HomeBloc 扩展 monthCount/totalCount 字段
- 日记卡片：72×72 预览图 + 标签摘要 + 心情圆点

## 🟠 路由 §3.12 + §3.13 拆分
- 新建 DiscoverPage (features/discover/views/discover_page.dart)
  - 搜索框（跳转 /search）
  - 每日推荐渐变卡片
  - 热门话题横向 chips（前 3 个 accent 高亮）
  - 精选模板 2 列网格
  - 达人日记列表
- /discover 路由从指向 SearchPage 改为 DiscoverPage
- 新增 /search 路由（全屏无 Tab）指向 SearchPage

## 🟠 Tab 栏 §2.2 重构
- 高度从 64px 改为 56+bottomPadding（含 safe-bottom，约 90px）
- 中心按钮从 CircularNotchedRectangle 凹槽改为 margin-top:-16px 凸起
- FAB 尺寸从默认改为 48×48 spec 规格
- FAB 图标从 edit_rounded 改为 add_rounded（spec §2.2）
- 删除未使用的 _navItems 旧常量

## 🟡 登录页圆角统一
- 移除 3 处 InputBorder 显式 mdBorder(16px) 覆盖
- 全局主题 smBorder(10px) 生效，对齐 spec
- 提交按钮圆角改为 pill（spec §2.6 Primary 按钮）

## 验证
- flutter analyze: 0 errors (剩余 40 个 warning/info 全为预存)
- flutter test: 84/85 通过（widget smoke test 预存失败，与本次无关）

app/lib/widgets/responsive_scaffold.dart

@@ -83,31 +83,7 @@ class _ResponsiveScaffoldState extends State<ResponsiveScaffold> {
   }
 }
 
-// ===== 导航项定义（4 项，中间由 FAB 占位）=====
-
-const _navItems = [
-  NavigationDestination(
-    icon: Icon(Icons.home_outlined),
-    selectedIcon: Icon(Icons.home),
-    label: '首页',
-  ),
-  NavigationDestination(
-    icon: Icon(Icons.calendar_month_outlined),
-    selectedIcon: Icon(Icons.calendar_month),
-    label: '日历',
-  ),
-  // 索引 2: 中心 FAB 占位（写日记）
-  NavigationDestination(
-    icon: Icon(Icons.explore_outlined),
-    selectedIcon: Icon(Icons.explore),
-    label: '发现',
-  ),
-  NavigationDestination(
-    icon: Icon(Icons.person_outline),
-    selectedIcon: Icon(Icons.person),
-    label: '我的',
-  ),
-];
+// ===== 导航项定义（平板/桌面 NavigationRail）=====
 
 const _railItems = [
   NavigationRailDestination(
@@ -132,7 +108,8 @@ const _railItems = [
   ),
 ];
 
-// ===== 中心写日记 FAB 按钮 =====
+// ===== 中心写日记 FAB 按钮（spec §2.2 凸起按钮）=====
+// 尺寸 48x48, 圆形, accent 色, shadow-accent
 
 class _CenterFabButton extends StatelessWidget {
   const _CenterFabButton({required this.onPressed});
@@ -141,19 +118,33 @@ class _CenterFabButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return FloatingActionButton(
-      heroTag: 'center_write',
-      onPressed: onPressed,
-      backgroundColor: AppColors.accent,
-      foregroundColor: const Color(0xFFFFF8F0),
-      elevation: 4,
+    return Material(
+      color: AppColors.accent,
       shape: const CircleBorder(),
-      child: const Icon(Icons.edit_rounded, size: 28),
+      elevation: 4,
+      shadowColor: AppColors.accent.withValues(alpha: 0.4),
+      child: InkWell(
+        onTap: onPressed,
+        customBorder: const CircleBorder(),
+        child: SizedBox(
+          width: 48,
+          height: 48,
+          child: Center(
+            child: Icon(Icons.add_rounded, size: 24, color: AppColors.bgLight),
+          ),
+        ),
+      ),
     );
   }
 }
 
-// ===== 手机布局 — 底部 TabBar + 中心凸起 FAB =====
+// ===== 手机布局 — 底部 TabBar (90px) + 中心凸起 FAB =====
+//
+// spec §2.2 规定：
+// - Tab 栏总高 = 56px (tab-height) + 34px (safe-bottom) = 90px
+// - 中心"写日记"按钮 margin-top:-16px 凸出 Tab 栏顶部
+// - 圆形 48x48, accent 色, shadow-accent
+// - Tab 项图标 24x24, 文字 11px/500
 
 class _MobileLayout extends StatelessWidget {
   const _MobileLayout({
@@ -177,85 +168,121 @@ class _MobileLayout extends StatelessWidget {
           ? AppBar(title: Text(appBarTitle!))
           : null,
       body: body,
-      floatingActionButton: onCenterButtonPressed != null
-          ? _CenterFabButton(onPressed: onCenterButtonPressed!)
-          : null,
-      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
+      extendBody: true, // 允许内容延伸到 Tab 栏下面（圆角透明效果）
       bottomNavigationBar: _BottomNavBar(
         selectedIndex: selectedIndex,
         onDestinationSelected: onDestinationSelected,
+        onCenterButtonPressed: onCenterButtonPressed,
       ),
     );
   }
 }
 
-/// 自定义底部导航栏 — 支持中心凹槽
+/// 自定义底部导航栏 — 90px 总高 + 中心凸起 FAB
 class _BottomNavBar extends StatelessWidget {
   const _BottomNavBar({
     required this.selectedIndex,
     required this.onDestinationSelected,
+    this.onCenterButtonPressed,
   });
 
   final int selectedIndex;
   final ValueChanged<int> onDestinationSelected;
+  final VoidCallback? onCenterButtonPressed;
 
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
     final colorScheme = theme.colorScheme;
+    final bottomPadding = MediaQuery.of(context).padding.bottom;
+    // spec §2.2: 总高 = 56 (tab-height) + bottomPadding (safe-bottom, 通常 34)
 
-    return BottomAppBar(
-      shape: const CircularNotchedRectangle(),
-      padding: EdgeInsets.zero,
-      height: 64,
-      color: colorScheme.surface,
-      surfaceTintColor: Colors.transparent,
-      child: Row(
-        mainAxisAlignment: MainAxisAlignment.spaceAround,
-        children: [
-          // 首页
-          _NavItem(
-            icon: Icons.home_outlined,
-            activeIcon: Icons.home,
-            label: '首页',
-            isSelected: selectedIndex == 0,
-            color: colorScheme.primary,
-            inactiveColor: colorScheme.onSurfaceVariant,
-            onTap: () => onDestinationSelected(0),
-          ),
-          // 日历
-          _NavItem(
-            icon: Icons.calendar_month_outlined,
-            activeIcon: Icons.calendar_month,
-            label: '日历',
-            isSelected: selectedIndex == 1,
-            color: colorScheme.primary,
-            inactiveColor: colorScheme.onSurfaceVariant,
-            onTap: () => onDestinationSelected(1),
-          ),
-          // 中间留给 FAB 凹槽 — 占位
-          const SizedBox(width: 48),
-          // 发现
-          _NavItem(
-            icon: Icons.explore_outlined,
-            activeIcon: Icons.explore,
-            label: '发现',
-            isSelected: selectedIndex == 2,
-            color: colorScheme.primary,
-            inactiveColor: colorScheme.onSurfaceVariant,
-            onTap: () => onDestinationSelected(2),
-          ),
-          // 我的
-          _NavItem(
-            icon: Icons.person_outline,
-            activeIcon: Icons.person,
-            label: '我的',
-            isSelected: selectedIndex == 3,
-            color: colorScheme.primary,
-            inactiveColor: colorScheme.onSurfaceVariant,
-            onTap: () => onDestinationSelected(3),
-          ),
-        ],
+    return Material(
+      color: Colors.transparent,
+      child: SizedBox(
+        height: 56 + bottomPadding,
+        child: Stack(
+          clipBehavior: Clip.none,
+          alignment: Alignment.topCenter,
+          children: [
+            // Tab 栏主体
+            Positioned(
+              left: 0,
+              right: 0,
+              top: 0,
+              bottom: 0,
+              child: Container(
+                decoration: BoxDecoration(
+                  color: colorScheme.surface,
+                  border: Border(
+                    top: BorderSide(color: colorScheme.outlineVariant, width: 1),
+                  ),
+                ),
+                padding: EdgeInsets.only(bottom: bottomPadding),
+                child: Row(
+                  children: [
+                    // 首页
+                    Expanded(
+                      child: _NavItem(
+                        icon: Icons.home_outlined,
+                        activeIcon: Icons.home,
+                        label: '首页',
+                        isSelected: selectedIndex == 0,
+                        color: colorScheme.primary,
+                        inactiveColor: colorScheme.onSurfaceVariant,
+                        onTap: () => onDestinationSelected(0),
+                      ),
+                    ),
+                    // 日历
+                    Expanded(
+                      child: _NavItem(
+                        icon: Icons.calendar_month_outlined,
+                        activeIcon: Icons.calendar_month,
+                        label: '日历',
+                        isSelected: selectedIndex == 1,
+                        color: colorScheme.primary,
+                        inactiveColor: colorScheme.onSurfaceVariant,
+                        onTap: () => onDestinationSelected(1),
+                      ),
+                    ),
+                    // 中间 FAB 占位
+                    const SizedBox(width: 64),
+                    // 发现
+                    Expanded(
+                      child: _NavItem(
+                        icon: Icons.explore_outlined,
+                        activeIcon: Icons.explore,
+                        label: '发现',
+                        isSelected: selectedIndex == 2,
+                        color: colorScheme.primary,
+                        inactiveColor: colorScheme.onSurfaceVariant,
+                        onTap: () => onDestinationSelected(2),
+                      ),
+                    ),
+                    // 我的
+                    Expanded(
+                      child: _NavItem(
+                        icon: Icons.person_outline,
+                        activeIcon: Icons.person,
+                        label: '我的',
+                        isSelected: selectedIndex == 3,
+                        color: colorScheme.primary,
+                        inactiveColor: colorScheme.onSurfaceVariant,
+                        onTap: () => onDestinationSelected(3),
+                      ),
+                    ),
+                  ],
+                ),
+              ),
+            ),
+            // 中心凸起写按钮 — margin-top:-16 凸出 Tab 栏顶部
+            if (onCenterButtonPressed != null)
+              Positioned(
+                top: -16,
+                child: _CenterFabButton(onPressed: onCenterButtonPressed!),
+              ),
+          ],
+        ),
       ),
     );
   }