Fix backend startup: add retry logic for DB init, proper logging, ensure all models imported before create_all, increase healthcheck start_period

backend/app/database.py

@@ -25,5 +25,8 @@ async def get_db():
 
 
 async def init_db():
+    # Import all models so their tables are registered on Base.metadata
+    import app.models  # noqa: F401
+
     async with engine.begin() as conn:
         await conn.run_sync(Base.metadata.create_all)