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/tests/test_model_registry.py

@@ -70,7 +70,7 @@ def test_empty_registry_no_files(tmp_path):
     import model_registry as reg
     with patch.object(config.settings, "home_dir", home):
         data = reg._load("scott")
-    assert data["version"] == 1
+    assert data["version"] == 2
     assert data["hosts"] == []
     assert data["models"] == []
     assert data["roles"] == {}
@@ -244,7 +244,7 @@ def test_migration_saves_registry_file(tmp_path):
         data2 = reg._load("scott")
 
     assert (home / "scott" / "model_registry.json").exists()
-    assert data2["version"] == 1
+    assert data2["version"] == 2
 
 
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