feat: model registry Phase 2 — cloud provider UI (Anthropic + Google)

Adds cloud provider management to /settings/models:
- Google Accounts section: add/remove Gemini API keys with labels
- Add Model form: provider tabs (Local / Google / Anthropic) with
  catalog dropdowns that auto-fill label and context_k
- Provider badges on model rows (Anthropic / Google / Local)
- /settings/local now redirects to /settings/models (canonical URL)
- save_cloud_model() in model_registry for Anthropic/Google entries
- Distill role migration restored in _migrate_from_local_llm
- Test fixes: version assertions updated to V2

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

cortex/llm_client.py

@@ -177,9 +177,9 @@ async def _local(system_prompt: str, messages: list[dict], model_cfg: dict | Non
     model   = cfg["model_name"]
 
     if not api_url:
-        raise RuntimeError("local_api_url not configured — set LOCAL_API_URL in .env or add a host at /settings/local")
+        raise RuntimeError("local_api_url not configured — set LOCAL_API_URL in .env or add a host at /settings/models")
     if not model:
-        raise RuntimeError("local_model not configured — add a model at /settings/local")
+        raise RuntimeError("local_model not configured — add a model at /settings/models")
 
     host_type = cfg.get("host_type", "openwebui")
     # "openwebui" uses Open WebUI/Ollama path layout; "openai" uses standard OpenAI layout