fix(api): correct tenant_id UUID handling in two list endpoints

[renjialin123]

Summary## Summary

GET /api/enterprise/llm-models returns HTTP 500 on upstream main even with a valid tenant and row in the DB.

Root cause: backend/app/api/enterprise.py:401 wraps the path parameter tid (already typed uuid.UUID, so FastAPI has already converted it) with uuid.UUID() again:

query = query.where(LLMModel.tenant_id == uuid.UUID(tid))   # ❌
# AttributeError: 'UUID' object has no attribute 'replace'
Fix (single line):

python
query = query.where(LLMModel.tenant_id == tid)             # ✅
No migration, no new dependency, no behaviour change for valid inputs. Independent of the db: Any = None regression (#841, being fixed by #847).

## Checklist

- [ ] Tested locally
- [ ] No unrelated changes included