refactor(08-02): switch cloud.py import to api.schemas.CloudConnectionOut

- Replace `from api.admin import CloudConnectionOut` with `from api.schemas import CloudConnectionOut`
- Eliminates cross-package coupling between api/cloud.py and api/admin.py (Pitfall 3)
- All 51 cloud + admin tests pass; CloudConnectionOut serialization unchanged
- Original definition in api/admin.py untouched until plan 08-04

backend/api/cloud.py

@@ -32,7 +32,7 @@ from pydantic import BaseModel
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from api.admin import CloudConnectionOut
+from api.schemas import CloudConnectionOut
 from config import settings
 from db.models import CloudConnection, User
 from deps.auth import get_regular_user