fix: reject startup when no provider configured instead of silent OpenRouter fallback (#10766)

When no provider was set in config.yaml and auto-detection found no
credentials, the agent silently fell back to bare OPENROUTER_API_KEY
from the environment and sent the configured model name to OpenRouter.
This produced undefined behavior -- wrong provider, wrong model routing,
and auxiliary tasks (compression, vision) hitting the wrong endpoint.

Fix: replace the silent fallback with a hard RuntimeError telling
the user to run hermes model or hermes setup. The provider must
be explicitly configured -- env vars are for secrets, not config.

run_agent.py

@@ -1021,16 +1021,12 @@ class AIAgent:
                             f"was found. Set the {_env_hint} environment "
                             f"variable, or switch to a different provider with `hermes model`."
                         )
-                    # Final fallback: try raw OpenRouter key
-                    client_kwargs = {
-                        "api_key": os.getenv("OPENROUTER_API_KEY", ""),
-                        "base_url": OPENROUTER_BASE_URL,
-                        "default_headers": {
-                            "HTTP-Referer": "https://hermes-agent.nousresearch.com",
-                            "X-OpenRouter-Title": "Hermes Agent",
-                            "X-OpenRouter-Categories": "productivity,cli-agent",
-                        },
-                    }
+                    # No provider configured — reject with a clear message.
+                    raise RuntimeError(
+                        "No LLM provider configured. Run `hermes model` to "
+                        "select a provider, or run `hermes setup` for first-time "
+                        "configuration."
+                    )
             
             self._client_kwargs = client_kwargs  # stored for rebuilding after interrupt