feat(app): D.3 中等优先级 UX 改进 — 保存指示器 + 触摸目标 + 主题持久化

D.3.2 三态保存指示器:
- 未保存 (灰色) → 保存中 (琥珀色脉冲点) → 已保存 (绿色点)
- _PulsingDot 动画组件，800ms 呼吸效果
- 点击'完成'时显示保存中状态

D.3.3 工具栏触摸目标:
- BoxConstraints 36x36 → 44x44，符合 WCAG 标准

D.3.4 主题偏好持久化:
- SettingsBloc 接受 SharedPreferences，保存/恢复 themeMode
- NuanjiApp 改为 StatefulWidget，异步初始化 SharedPreferences
- 启动时显示 loading，初始化完成后渲染 app

app/lib/features/editor/views/editor_page.dart

@@ -337,6 +337,9 @@ class _EditorViewState extends State<_EditorView> {
   /// 查看模式：打开已有日记时默认只读，点击"编辑"后进入编辑模式
   bool _isViewMode = false;
 
+  /// 保存中状态 — 用于显示"保存中..."指示器
+  bool _isSaving = false;
+
   @override
   void initState() {
     super.initState();
@@ -595,9 +598,16 @@ class _EditorViewState extends State<_EditorView> {
     );
   }
 
-  /// 保存处理
+  /// 保存处理 — 显示"保存中..."后触发保存
   void _handleSave(BuildContext context, EditorState state) {
-    widget.onSaveComplete();
+    setState(() => _isSaving = true);
+    // 短暂延迟让 UI 显示"保存中..."状态
+    Future.delayed(const Duration(milliseconds: 300), () {
+      if (mounted) {
+        setState(() => _isSaving = false);
+        widget.onSaveComplete();
+      }
+    });
   }
 
   /// 显示评论列表
@@ -624,7 +634,26 @@ class _EditorViewState extends State<_EditorView> {
   }
 
   /// 自动保存状态指示器
+  /// 保存指示器 — 三态: 未保存 / 保存中 / 已保存
   Widget _buildAutosaveIndicator(EditorState state) {
+    // 保存中 — 琥珀色脉冲点
+    if (_isSaving) {
+      return Padding(
+        padding: const EdgeInsets.symmetric(horizontal: 4),
+        child: Row(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            _PulsingDot(color: AppColors.tertiary),
+            const SizedBox(width: 4),
+            Text(
+              '保存中...',
+              style: TextStyle(fontSize: 11, color: Colors.amber[700]),
+            ),
+          ],
+        ),
+      );
+    }
+    // 未保存
     if (state.lastSavedAt == null) {
       return Padding(
         padding: const EdgeInsets.symmetric(horizontal: 4),
@@ -634,6 +663,7 @@ class _EditorViewState extends State<_EditorView> {
         ),
       );
     }
+    // 已保存 — 绿色点
     return Padding(
       padding: const EdgeInsets.symmetric(horizontal: 4),
       child: Row(
@@ -1211,3 +1241,53 @@ class _ImageSourceButton extends StatelessWidget {
     );
   }
 }
+
+/// 脉冲圆点动画 — 用于"保存中..."指示器
+class _PulsingDot extends StatefulWidget {
+  const _PulsingDot({required this.color});
+  final Color color;
+
+  @override
+  State<_PulsingDot> createState() => _PulsingDotState();
+}
+
+class _PulsingDotState extends State<_PulsingDot>
+    with SingleTickerProviderStateMixin {
+  late final AnimationController _controller;
+
+  @override
+  void initState() {
+    super.initState();
+    _controller = AnimationController(
+      vsync: this,
+      duration: const Duration(milliseconds: 800),
+    )..repeat(reverse: true);
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedBuilder(
+      animation: _controller,
+      builder: (context, _) {
+        final scale = 0.6 + 0.4 * _controller.value;
+        return Transform.scale(
+          scale: scale,
+          child: Container(
+            width: 6,
+            height: 6,
+            decoration: BoxDecoration(
+              color: widget.color,
+              shape: BoxShape.circle,
+            ),
+          ),
+        );
+      },
+    );
+  }
+}

app/lib/features/editor/widgets/editor_toolbar.dart

@@ -71,7 +71,7 @@ class EditorToolbar extends StatelessWidget {
       onTap: () => onEvent(isActive ? ToolReactivated(tool) : ToolChanged(tool)),
       behavior: HitTestBehavior.opaque,
       child: Container(
-        constraints: const BoxConstraints(minWidth: 36, minHeight: 36),
+        constraints: const BoxConstraints(minWidth: 44, minHeight: 44),
         padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
         child: Column(
           mainAxisSize: MainAxisSize.min,