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/static/settings.html

@@ -302,7 +302,7 @@
       <p style="font-size:0.8rem; color:#94a3b8; margin-bottom:0.85rem; line-height:1.55;">
         Configure OpenAI-compatible hosts and models (Open WebUI, Ollama, LM Studio, etc.).
       </p>
-      <a href="/settings/local"
+      <a href="/settings/models"
          style="display:inline-block; padding:0.55rem 1rem; background:#7c3aed; border-radius:6px;
                 color:#fff; font-size:0.88rem; font-weight:600; text-decoration:none;
                 transition:background 0.15s;">