Never resolve to a disabled endpoint model (#861)

Background tasks (e.g. the Email Tags / check_email_urgency action)
resolve their model through resolve_endpoint("utility") → Default Chat.
When the configured model is one the user has since disabled on the
endpoint, the resolver still dispatched to it — on Groq that surfaces as
every email failing with "HTTP 400: model ... requires terms acceptance".

Two paths fed this:
- The auto-pick fallback selected from cached_models without excluding
  the endpoint's hidden_models, so a disabled model listed first won.
- A stale default_model left pointing at a now-disabled model (seeded at
  endpoint registration from raw model_ids[0]) was used verbatim.

Fix resolve_endpoint / resolve_endpoint_by_id to drop a configured model
that's in hidden_models and to pick the first ENABLED chat model. Also
seed default_model on registration via _first_chat_model so we never pin
the global default to an embedding/tts entry a provider lists first.

Checks: python -m pytest tests/test_endpoint_resolver.py
        tests/test_model_routes.py tests/test_model_context.py (all pass);
        python -m py_compile app.py routes/model_routes.py
        src/endpoint_resolver.py.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

routes/model_routes.py

@@ -1052,11 +1052,15 @@ def setup_model_routes(model_discovery):
             )
             db.add(ep)
             db.commit()
-            # Auto-set as default chat endpoint if none configured yet
+            # Auto-set as default chat endpoint if none configured yet. Seed
+            # the first CHAT model (not raw model_ids[0]) so we don't pin the
+            # global default to an embedding/tts/etc. entry a provider happens
+            # to list first.
             settings = _load_settings()
             if not settings.get("default_endpoint_id"):
+                from src.endpoint_resolver import _first_chat_model
                 settings["default_endpoint_id"] = ep.id
-                settings["default_model"] = model_ids[0] if model_ids else ""
+                settings["default_model"] = _first_chat_model(model_ids) or ""
                 _save_settings(settings)
             _invalidate_models_cache()
             _local_probe_cache["data"] = None