fix: 防止新依赖缺失导致后端启动崩溃

scheduler和reports模块加载失败时不再拖垮整个应用，
核心功能(登录/项目/提交)可正常使用。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/main.py

@@ -41,7 +41,11 @@ from routers.submissions import router as submissions_router
 from routers.costs import router as costs_router
 from routers.dashboard import router as dashboard_router
 from routers.roles import router as roles_router
-from routers.reports import router as reports_router
+try:
+    from routers.reports import router as reports_router
+except ImportError as e:
+    reports_router = None
+    logging.warning(f"[路由] reports 模块加载失败: {e}")
 
 app.include_router(auth_router)
 app.include_router(users_router)
@@ -50,7 +54,8 @@ app.include_router(submissions_router)
 app.include_router(costs_router)
 app.include_router(dashboard_router)
 app.include_router(roles_router)
-app.include_router(reports_router)
+if reports_router:
+    app.include_router(reports_router)
 
 # 前端静态文件
 frontend_dir = os.path.join(os.path.dirname(os.path.dirname(__file__)), "frontend", "dist")
@@ -68,16 +73,22 @@ if os.path.exists(frontend_dir):
 @app.on_event("startup")
 async def start_scheduler():
     """启动定时任务调度器"""
+    try:
         from services.scheduler_service import setup_scheduler
         setup_scheduler()
+    except Exception as e:
+        logger.warning(f"[定时任务] 启动失败（不影响核心功能）: {e}")
 
 
 @app.on_event("shutdown")
 async def stop_scheduler():
     """关闭定时任务调度器"""
+    try:
         from services.scheduler_service import scheduler
         scheduler.shutdown(wait=False)
         logger.info("[定时任务] 已关闭")
+    except Exception:
+        pass
 
 
 @app.on_event("startup")