fix(model): preserve custom endpoint credentials and accept cloud models not in /v1/models

When switching models on a custom endpoint (ollama-launch):
- Same-provider switches no longer re-resolve credentials (fixes base_url
  being lost for 'custom' provider on subsequent switches)
- Named providers (ollama-launch) are resolved via user_providers so
  switch_model can find their base_url from config
- Models not in the /v1/models probe but present in the user's saved
  provider config are accepted with a warning instead of rejected
- CLI /model and TUI /model both pass user_providers/custom_providers
  to switch_model so the config model list is available for validation

Closes #15088

cli.py

@@ -5270,24 +5270,22 @@ class HermesCLI:
         # Parse --provider and --global flags
         model_input, explicit_provider, persist_global = parse_model_flags(raw_args)
 
+        # Load providers for switch_model (picker path needs them below)
         user_provs = None
         custom_provs = None
+        try:
+            from hermes_cli.config import get_compatible_custom_providers, load_config
+            cfg = load_config()
+            user_provs = cfg.get("providers")
+            custom_provs = get_compatible_custom_providers(cfg)
+        except Exception:
+            pass
 
         # No args at all: open prompt_toolkit-native picker modal
         if not model_input and not explicit_provider:
             model_display = self.model or "unknown"
             provider_display = get_label(self.provider) if self.provider else "unknown"
 
-            user_provs = None
-            custom_provs = None
-            try:
-                from hermes_cli.config import get_compatible_custom_providers, load_config
-                cfg = load_config()
-                user_provs = cfg.get("providers")
-                custom_provs = get_compatible_custom_providers(cfg)
-            except Exception:
-                pass
-
             try:
                 providers = list_authenticated_providers(
                     current_provider=self.provider or "",