Backend enhancements: auth, channels, restaurants, daemon improvements

- Add admin auth dependency and role checks
- Expand channel and restaurant API routes
- Improve YouTube transcript fetching
- Enhance daemon worker with better error handling and scheduling

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

backend/api/deps.py

@@ -30,3 +30,11 @@ def get_optional_user(authorization: str = Header(None)) -> dict | None:
         return verify_jwt(token)
     except Exception:
         return None
+
+
+def get_admin_user(authorization: str = Header(None)) -> dict:
+    """Require authenticated admin user. Raises 401/403."""
+    user = get_current_user(authorization)
+    if not user.get("is_admin"):
+        raise HTTPException(403, "관리자 권한이 필요합니다")
+    return user