fix: include custom_providers in /model command listings and resolution

Custom providers defined in config.yaml under  were
completely invisible to the /model command in both gateway (Telegram,
Discord, etc.) and CLI. The provider listing skipped them and explicit
switching via --provider failed with "Unknown provider".

Root cause: gateway/run.py, cli.py, and model_switch.py only read the
 dict from config, ignoring  entirely.

Changes:
- providers.py: add resolve_custom_provider() and extend
  resolve_provider_full() to check custom_providers after user_providers
- model_switch.py: propagate custom_providers through switch_model(),
  list_authenticated_providers(), and get_authenticated_provider_slugs();
  add custom provider section to provider listings
- gateway/run.py: read custom_providers from config, pass to all
  model-switch calls
- cli.py: hoist config loading, pass custom_providers to listing and
  switch calls

Tests: 4 new regression tests covering listing, resolution, and gateway
command handler. All 71 tests pass.

hermes_cli/providers.py

@@ -452,9 +452,55 @@ def resolve_user_provider(name: str, user_config: Dict[str, Any]) -> Optional[Pr
     )
 
 
+def resolve_custom_provider(
+    name: str,
+    custom_providers: Optional[List[Dict[str, Any]]],
+) -> Optional[ProviderDef]:
+    """Resolve a provider from the user's config.yaml ``custom_providers`` list."""
+    if not custom_providers or not isinstance(custom_providers, list):
+        return None
+
+    requested = (name or "").strip().lower()
+    canonical = normalize_provider(name)
+    if not requested:
+        return None
+
+    for entry in custom_providers:
+        if not isinstance(entry, dict):
+            continue
+
+        display_name = (entry.get("name") or "").strip()
+        api_url = (
+            entry.get("base_url", "")
+            or entry.get("url", "")
+            or entry.get("api", "")
+            or ""
+        ).strip()
+        if not display_name or not api_url:
+            continue
+
+        slug = "custom:" + display_name.lower().replace(" ", "-")
+        if requested not in {display_name.lower(), slug, canonical}:
+            continue
+
+        return ProviderDef(
+            id=slug,
+            name=display_name,
+            transport="openai_chat",
+            api_key_env_vars=(),
+            base_url=api_url,
+            is_aggregator=False,
+            auth_type="api_key",
+            source="user-config",
+        )
+
+    return None
+
+
 def resolve_provider_full(
     name: str,
     user_providers: Optional[Dict[str, Any]] = None,
+    custom_providers: Optional[List[Dict[str, Any]]] = None,
 ) -> Optional[ProviderDef]:
     """Full resolution chain: built-in → models.dev → user config.
 
@@ -463,6 +509,7 @@ def resolve_provider_full(
     Args:
         name: Provider name or alias.
         user_providers: The ``providers:`` dict from config.yaml (optional).
+        custom_providers: The ``custom_providers:`` list from config.yaml (optional).
 
     Returns:
         ProviderDef if found, else None.
@@ -485,6 +532,11 @@ def resolve_provider_full(
         if user_pdef is not None:
             return user_pdef
 
+    # 2b. Saved custom providers from config
+    custom_pdef = resolve_custom_provider(name, custom_providers)
+    if custom_pdef is not None:
+        return custom_pdef
+
     # 3. Try models.dev directly (for providers not in our ALIASES)
     try:
         from agent.models_dev import get_provider_info as _mdev_provider