Add event routes and enhance routing structure

Introduced routes for event management, including CRUD operations and querying by user or public visibility. Updated event themes routes with operation IDs for better documentation. Refactored `api/main.py` to `api/router.py` and integrated events routing into the API.

backend/app/main.py

@@ -5,7 +5,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import HTMLResponse
 
-from app.api.main import api_router
+from app.api.router import api_router
 from app.core.config import settings
 
 scheduler = AsyncIOScheduler()