fix: multi-provider model routing via @provider: hint (#138) (#146)

The previous fix (#142) prefixed non-default provider models with
'provider/model' which then hit the cross-provider guard and routed
to OpenRouter — worse than before for users without an OpenRouter key.

New approach: non-default provider models use '@provider:model' format
(e.g. @minimax:MiniMax-M2.7). resolve_model_provider() parses this
hint and returns (bare_model, provider, None). streaming.py and
routes.py then pass the resolved provider to
resolve_runtime_provider(requested=provider) which gets the correct
per-provider API key and base_url from hermes-agent.

This uses the agent's own credential resolution instead of reinventing
routing logic in the webui.

Fixes #138

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

api/streaming.py

@@ -143,11 +143,12 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
                 raise ImportError("AIAgent not available -- check that hermes-agent is on sys.path")
             resolved_model, resolved_provider, resolved_base_url = resolve_model_provider(model)
 
-            # Resolve API key via Hermes runtime provider (matches gateway behaviour)
+            # Resolve API key via Hermes runtime provider (matches gateway behaviour).
+            # Pass the resolved provider so non-default providers get their own credentials.
             resolved_api_key = None
             try:
                 from hermes_cli.runtime_provider import resolve_runtime_provider
-                _rt = resolve_runtime_provider()
+                _rt = resolve_runtime_provider(requested=resolved_provider)
                 resolved_api_key = _rt.get("api_key")
                 if not resolved_provider:
                     resolved_provider = _rt.get("provider")