fix: model dropdown missing custom/configured models (#116, #117)

Two related bugs in get_available_models():

1. cfg_base_url undefined for string model configs (#117):
   cfg_base_url was defined inside 'elif isinstance(model_cfg, dict)'
   but referenced unconditionally at line 506. If model config was a
   plain string, NameError crashed model detection. Fix: initialize
   cfg_base_url='' before the conditional.

2. Configured default_model missing from dropdown (#116):
   The OpenRouter branch substituted _FALLBACK_MODELS without checking
   if the user's model.default was in the list. Models like
   'openrouter/free' or custom local models were invisible. Fix: after
   building all groups, check if default_model is present. If not,
   inject it at the top of the matching provider group.

Closes #116, closes #117

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/config.py

@@ -426,6 +426,7 @@ def get_available_models() -> dict:
     groups = []
 
     # 1. Read config.yaml model section
+    cfg_base_url = ''  # must be defined before conditional blocks (#117)
     model_cfg = cfg.get('model', {})
     cfg_base_url = ''
     if isinstance(model_cfg, str):
@@ -607,6 +608,25 @@ def get_available_models() -> dict:
         for provider_name, models in by_provider.items():
             groups.append({'provider': provider_name, 'models': models})
 
+    # Ensure the user's configured default_model always appears in the dropdown.
+    # It may be missing if the model isn't in any hardcoded list (e.g. openrouter/free,
+    # a custom local model, or any model.default not in _FALLBACK_MODELS).
+    if default_model:
+        all_ids = {m['id'] for g in groups for m in g.get('models', [])}
+        if default_model not in all_ids:
+            # Determine which group to inject into
+            label = default_model.split('/')[-1] if '/' in default_model else default_model
+            injected = False
+            for g in groups:
+                if active_provider and active_provider.lower() in g.get('provider', '').lower():
+                    g['models'].insert(0, {'id': default_model, 'label': label})
+                    injected = True
+                    break
+            if not injected and groups:
+                groups[0]['models'].insert(0, {'id': default_model, 'label': label})
+            elif not groups:
+                groups.append({'provider': active_provider or 'Default', 'models': [{'id': default_model, 'label': label}]})
+
     return {
         'active_provider': active_provider,
         'default_model': default_model,