fix(app): 修复 P2~P4 共 10 项前端问题

P2 必须修复:
- 教师布置主题 classId 从硬编码改为班级下拉选择器
- 班级日记墙使用服务端 classId 过滤替代前端过滤
- Profile 统计栏接入 JournalRepository 真实数据
- WeeklyPage 从全硬编码改为 JournalRepository 数据驱动

P3 建议改进:
- 提取 mood_utils.dart 公共函数，消除 4 处重复定义
- 贴纸库搜索框连接 StickerBloc 按名称过滤

P4 细节打磨:
- 家长页多孩子时显示 DropdownButton 选择器
- 搜索结果日记卡片点击跳转 /editor?id=
- MonthlyPage 照片数量从 JournalElement 统计
- calendar_page/mood_page/search_page 统一使用 moodToEmoji/moodToLabel

app/lib/features/class_/bloc/class_bloc.dart

@@ -261,11 +261,9 @@ class ClassBloc extends Bloc<ClassEvent, ClassState> {
     emit(current.copyWith(isLoadingWall: true));
 
     try {
-      // 加载属于该班级的公开日记
-      final journals = await _journalRepo.getJournals();
-      final classJournals = journals
-          .where((j) => j.classId == event.classId && j.sharedToClass)
-          .toList();
+      // 服务端过滤：按 classId 查询班级公开日记（后端 API 已支持 ?class_id= 参数）
+      final journals = await _journalRepo.getJournals(classId: event.classId);
+      final classJournals = journals.where((j) => j.sharedToClass).toList();
 
       emit(current.copyWith(diaryWall: classJournals, isLoadingWall: false));
     } catch (_) {
@@ -345,9 +343,6 @@ class ClassBloc extends Bloc<ClassEvent, ClassState> {
     TopicAssign event,
     Emitter<ClassState> emit,
   ) async {
-    if (state is! ClassDetailLoaded) return;
-    final current = state as ClassDetailLoaded;
-
     try {
       final dto = await _classRepo.assignTopic(
         classId: event.classId,
@@ -355,15 +350,20 @@ class ClassBloc extends Bloc<ClassEvent, ClassState> {
         description: event.description,
         dueDate: event.dueDate,
       );
-      final newTopic = TopicAssignment(
-        id: dto.id,
-        classId: dto.classId,
-        teacherId: dto.teacherId,
-        title: dto.title,
-        description: dto.description,
-        dueDate: dto.dueDate,
-      );
-      emit(current.copyWith(topics: [newTopic, ...current.topics]));
+
+      // 更新本地 topics 列表（仅在班级详情视图中）
+      if (state is ClassDetailLoaded) {
+        final current = state as ClassDetailLoaded;
+        final newTopic = TopicAssignment(
+          id: dto.id,
+          classId: dto.classId,
+          teacherId: dto.teacherId,
+          title: dto.title,
+          description: dto.description,
+          dueDate: dto.dueDate,
+        );
+        emit(current.copyWith(topics: [newTopic, ...current.topics]));
+      }
     } catch (_) {
       // 静默失败
     }