feat(app): 共享 UI 组件 + 4 个关键 UX bug 修复

Phase 0 — 共享组件:
- EmptyStateWidget: 统一空状态 (icon + title + subtitle + CTA)
- ErrorStateWidget: 统一错误状态 (message + retry)
- SkeletonBox + SkeletonList: 统一骨架屏加载 (shimmer 动画)

Phase 1 — Bug 修复:
- 班级评论按 journalId 过滤，避免显示在错误日记卡片下
- moodCellColors key 修正: love/tired → angry/thinking
- 日历非 CalendarLoaded 状态改为加载指示器 (不再 SizedBox.shrink)
- 贴纸数统计改为 '--' 占位 (之前错误显示日记总数)

app/lib/features/profile/views/profile_page.dart

@@ -425,7 +425,7 @@ class _LiveStatsBarState extends State<_LiveStatsBar> {
           VerticalDivider(width: 1, indent: 4, endIndent: 4, color: widget.borderSoft),
           _StatItem(label: '本月日记', value: '$_monthCount', valueColor: widget.colorScheme.onSurface),
           VerticalDivider(width: 1, indent: 4, endIndent: 4, color: widget.borderSoft),
-          _StatItem(label: '贴纸数', value: _totalCount > 0 ? '$_totalCount' : '0', valueColor: widget.colorScheme.onSurface),
+          _StatItem(label: '贴纸数', value: '--', valueColor: widget.colorScheme.onSurface),
         ],
       ),
     );