feat: add forum seed categories, improve page layouts and navigation

- Seed default forum categories (announcements, learning, feedback) on startup
- Update forum pages with improved category/post/reply UI
- Refine navbar, mobile nav, and home page content layout
- Improve analytics, course-content, knowledge, profile, settings, spatial pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/main.py

@@ -56,6 +56,36 @@ def startup_knowledge_base():
     except Exception as e:
         print(f"启动知识库文件监控服务失败: {str(e)}")
 
+
+def seed_forum_categories():
+    """初始化论坛默认分类"""
+    from src.core.database import get_db
+    from src.models.forum import ForumCategory
+
+    DEFAULT_CATEGORIES = [
+        {"slug": "announcements", "name": "课程公告", "description": "课程通知、作业安排与重要信息"},
+        {"slug": "course-learning", "name": "学习讨论", "description": "交流学习心得，讨论课程内容与难点"},
+        {"slug": "system-feedback", "name": "使用反馈", "description": "分享系统使用经验，提出改进建议"},
+    ]
+
+    db = next(get_db())
+    try:
+        existing_count = db.query(ForumCategory).count()
+        if existing_count > 0:
+            print(f"论坛分类已存在（{existing_count} 个），跳过初始化")
+            return
+
+        for cat_data in DEFAULT_CATEGORIES:
+            category = ForumCategory(**cat_data)
+            db.add(category)
+        db.commit()
+        print(f"已创建 {len(DEFAULT_CATEGORIES)} 个论坛分类")
+    except Exception as e:
+        db.rollback()
+        print(f"初始化论坛分类失败: {e}")
+    finally:
+        db.close()
+
 # 应用启动事件
 @app.on_event("startup")
 async def startup_event():
@@ -97,6 +127,12 @@ async def startup_event():
         startup_knowledge_base()
     except Exception as e:
         print(f"启动知识库服务失败: {e}", file=sys.stderr)
+
+    # 初始化论坛分类
+    try:
+        seed_forum_categories()
+    except Exception as e:
+        print(f"初始化论坛分类失败: {e}", file=sys.stderr)
         sys.stderr.flush()
     
     print("应用启动事件完成", file=sys.stderr)