feat(app): 发现页动态化 — DiscoverBloc + API 驱动 + 下拉刷新

- 新增 DiscoverBloc (LoadData/Refresh) + DiscoverModels 4 个数据类
- DiscoverPage 改为 BlocBuilder 驱动: loading/loaded/error/empty 四态
- 替换全部硬编码占位数据为 API 实时数据
- 添加 RefreshIndicator 下拉刷新
- 离线异常时保留已有数据，友好错误提示

app/lib/features/discover/models/discover_models.dart

@@ -0,0 +1,160 @@
+// 发现页数据模型 — 手写不可变类（避免 build_runner 依赖）
+
+/// 发现页聚合响应 — 一次 API 返回全部板块数据
+class DiscoverData {
+  final InspirationItem? dailyInspiration;
+  final List<TagCount> hotTopics;
+  final List<DiscoverTemplateItem> featuredTemplates;
+  final List<ExpertDiaryItem> expertDiaries;
+
+  const DiscoverData({
+    this.dailyInspiration,
+    this.hotTopics = const [],
+    this.featuredTemplates = const [],
+    this.expertDiaries = const [],
+  });
+
+  factory DiscoverData.fromJson(Map<String, dynamic> json) => DiscoverData(
+        dailyInspiration: json['daily_inspiration'] != null
+            ? InspirationItem.fromJson(
+                json['daily_inspiration'] as Map<String, dynamic>)
+            : null,
+        hotTopics: (json['hot_topics'] as List? ?? [])
+            .map((e) => TagCount.fromJson(e as Map<String, dynamic>))
+            .toList(),
+        featuredTemplates: (json['featured_templates'] as List? ?? [])
+            .map(
+                (e) => DiscoverTemplateItem.fromJson(e as Map<String, dynamic>))
+            .toList(),
+        expertDiaries: (json['expert_diaries'] as List? ?? [])
+            .map((e) => ExpertDiaryItem.fromJson(e as Map<String, dynamic>))
+            .toList(),
+      );
+
+  /// 心情 → emoji 映射
+  static String moodToEmoji(String mood) => switch (mood) {
+        'happy' => '😊',
+        'calm' => '😌',
+        'sad' => '😢',
+        'angry' => '😤',
+        'thinking' => '🤔',
+        _ => '📝',
+      };
+}
+
+/// 每日推荐条目
+class InspirationItem {
+  final String journalId;
+  final String title;
+  final String authorName;
+  final String mood;
+  final DateTime date;
+
+  const InspirationItem({
+    required this.journalId,
+    required this.title,
+    required this.authorName,
+    required this.mood,
+    required this.date,
+  });
+
+  factory InspirationItem.fromJson(Map<String, dynamic> json) =>
+      InspirationItem(
+        journalId: json['journal_id'] as String,
+        title: json['title'] as String,
+        authorName: json['author_name'] as String,
+        mood: json['mood'] as String,
+        date: DateTime.parse(json['date'] as String),
+      );
+}
+
+/// 热门话题
+class TagCount {
+  final String tag;
+  final int count;
+
+  const TagCount({required this.tag, required this.count});
+
+  factory TagCount.fromJson(Map<String, dynamic> json) => TagCount(
+        tag: json['tag'] as String,
+        count: json['count'] as int,
+      );
+}
+
+/// 精选模板条目（轻量版，不含 layout_data）
+class DiscoverTemplateItem {
+  final String id;
+  final String name;
+  final String? previewUrl;
+  final String? category;
+  final bool isFree;
+
+  const DiscoverTemplateItem({
+    required this.id,
+    required this.name,
+    this.previewUrl,
+    this.category,
+    this.isFree = true,
+  });
+
+  factory DiscoverTemplateItem.fromJson(Map<String, dynamic> json) =>
+      DiscoverTemplateItem(
+        id: json['id'] as String,
+        name: json['name'] as String,
+        previewUrl: json['preview_url'] as String?,
+        category: json['category'] as String?,
+        isFree: json['is_free'] as bool? ?? true,
+      );
+
+  /// 分类 → emoji 映射
+  String get emoji => switch (category) {
+        '日常' => '📖',
+        '旅行' => '✈️',
+        '校园' => '🎓',
+        '节日' => '🎄',
+        '创意' => '✨',
+        '心情' => '🌿',
+        _ => '📝',
+      };
+
+  /// 使用人数展示文本
+  String get usageText => isFree ? '免费模板' : '精品模板';
+}
+
+/// 达人日记条目
+class ExpertDiaryItem {
+  final String journalId;
+  final String title;
+  final String authorId;
+  final String authorName;
+  final String authorEmoji;
+  final String contentPreview;
+  final int likeCount;
+  final DateTime createdAt;
+
+  const ExpertDiaryItem({
+    required this.journalId,
+    required this.title,
+    required this.authorId,
+    required this.authorName,
+    required this.authorEmoji,
+    required this.contentPreview,
+    required this.likeCount,
+    required this.createdAt,
+  });
+
+  factory ExpertDiaryItem.fromJson(Map<String, dynamic> json) =>
+      ExpertDiaryItem(
+        journalId: json['journal_id'] as String,
+        title: json['title'] as String,
+        authorId: json['author_id'] as String,
+        authorName: json['author_name'] as String,
+        authorEmoji: json['author_emoji'] as String,
+        contentPreview: json['content_preview'] as String? ?? '',
+        likeCount: json['like_count'] as int? ?? 0,
+        createdAt: DateTime.parse(json['created_at'] as String),
+      );
+
+  /// 点赞数展示文本
+  String get likeText => '$likeCount 赞';
+}