fix(runtime_provider): _get_named_custom_provider must honour transport field on v12+ providers dict

The v11→v12 migrate_config step writes the API mode for every entry
under the new transport: field (per the v12+ schema in
_normalize_custom_provider_entry).  _get_named_custom_provider
read the legacy api_mode: spelling only, so for every migrated
config the lookup returned None for the api mode.

Downstream, _resolve_named_custom_runtime then falls back through
custom_provider.get("api_mode") or _detect_api_mode_for_url(base_url)
or "chat_completions".  For loopback URLs (proxies, local servers)
or unknown hostnames, the URL detector returns None and the resolver
silently downgrades the configured codex_responses /
anthropic_messages transport to chat_completions.  Requests
get sent to /v1/chat/completions instead of /v1/responses or
/v1/messages and the provider 404s — or worse, returns a usable
chat_completions response while skipping the model's reasoning /
caching surface.

Fix: read both field names — entry.get("api_mode") or
entry.get("transport") — at the two match-by-key + match-by-name
branches in _get_named_custom_provider.  The runtime normaliser
_normalize_custom_provider_entry already accepts both spellings;
this lifts the same compat into the direct-dict reader so v12+
configs work without going through the shim.

Adds three regression tests under
tests/hermes_cli/test_user_providers_model_switch.py:
- transport field is read on the match-by-key branch
- legacy api_mode spelling still works for hand-edited configs
- transport is read on the match-by-display-name branch

hermes_cli/runtime_provider.py

@@ -391,7 +391,14 @@ def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, An
                         "api_key": resolved_api_key,
                         "model": entry.get("default_model", ""),
                     }
-                    api_mode = _parse_api_mode(entry.get("api_mode"))
+                    # The v11→v12 migration writes the API mode under the new
+                    # ``transport`` field, but hand-edited configs may still
+                    # use the legacy ``api_mode`` spelling.  Accept both —
+                    # the runtime normaliser ``_normalize_custom_provider_entry``
+                    # already does, so without this lift every migrated config
+                    # silently downgrades codex_responses / anthropic_messages
+                    # providers to chat_completions in the resolved runtime.
+                    api_mode = _parse_api_mode(entry.get("api_mode") or entry.get("transport"))
                     if api_mode:
                         result["api_mode"] = api_mode
                     return result
@@ -409,7 +416,7 @@ def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, An
                             "api_key": resolved_api_key,
                             "model": entry.get("default_model", ""),
                         }
-                        api_mode = _parse_api_mode(entry.get("api_mode"))
+                        api_mode = _parse_api_mode(entry.get("api_mode") or entry.get("transport"))
                         if api_mode:
                             result["api_mode"] = api_mode
                         return result