feat(providers): make all 33 providers pluggable under plugins/model-providers/

Every provider profile is now a self-contained plugin under
plugins/model-providers/<name>/, mirroring the plugins/platforms/
pattern established for IRC and Teams. The ProviderProfile ABC
stays in providers/; the per-provider profile data moves out.

- plugins/model-providers/<name>/__init__.py calls register_provider()
- plugins/model-providers/<name>/plugin.yaml declares kind: model-provider
- providers/__init__.py._discover_providers() lazily scans bundled plugins
  then $HERMES_HOME/plugins/model-providers/<name>/ (user override path)
- User plugins with the same name override bundled ones (last-writer-wins
  in register_provider)
- Legacy providers/<name>.py layout still supported for back-compat with
  out-of-tree editable installs
- Hermes PluginManager: new kind=model-provider; skipped like memory
  plugins (providers/ discovery owns them); standalone plugins with
  register_provider+ProviderProfile in their __init__.py auto-coerce to
  this kind (same heuristic as memory providers)
- skip_names extended to include 'model-providers' so the general
  PluginManager doesn't double-scan the category
- 4 new tests in tests/providers/test_plugin_discovery.py covering
  bundled discovery, user override, and general-loader isolation
- Docs updated: website/docs/developer-guide/adding-providers.md,
  provider-runtime.md, providers/README.md, plugins/model-providers/README.md

No API break: auth.py / config.py / doctor.py / models.py / runtime_provider.py /
model_metadata.py / auxiliary_client.py / chat_completions.py / run_agent.py
all still consume providers via get_provider_profile() / list_providers() —
they just now see plugin-discovered entries instead of pkgutil-iterated ones.

Third parties can now drop a single directory into
~/.hermes/plugins/model-providers/<name>/ to add or override an inference
provider without touching the repo.

plugins/model-providers/openrouter/__init__.py

@@ -0,0 +1,86 @@
+"""OpenRouter provider profile."""
+
+import logging
+from typing import Any
+
+from providers import register_provider
+from providers.base import ProviderProfile
+
+logger = logging.getLogger(__name__)
+
+_CACHE: list[str] | None = None
+
+
+class OpenRouterProfile(ProviderProfile):
+    """OpenRouter aggregator — provider preferences, reasoning config passthrough."""
+
+    def fetch_models(
+        self,
+        *,
+        api_key: str | None = None,
+        timeout: float = 8.0,
+    ) -> list[str] | None:
+        """Fetch from public OpenRouter catalog — no auth required.
+
+        Note: Tool-call capability filtering is applied by hermes_cli/models.py
+        via fetch_openrouter_models() → _openrouter_model_supports_tools(), not
+        here. The picker early-returns via the dedicated openrouter path before
+        reaching this method, so filtering here would be unreachable.
+        """
+        global _CACHE  # noqa: PLW0603
+        if _CACHE is not None:
+            return _CACHE
+        try:
+            result = super().fetch_models(api_key=None, timeout=timeout)
+            if result is not None:
+                _CACHE = result
+            return result
+        except Exception as exc:
+            logger.debug("fetch_models(openrouter): %s", exc)
+            return None
+
+    def build_extra_body(
+        self, *, session_id: str | None = None, **context: Any
+    ) -> dict[str, Any]:
+        body: dict[str, Any] = {}
+        prefs = context.get("provider_preferences")
+        if prefs:
+            body["provider"] = prefs
+        return body
+
+    def build_api_kwargs_extras(
+        self,
+        *,
+        reasoning_config: dict | None = None,
+        supports_reasoning: bool = False,
+        **context: Any,
+    ) -> tuple[dict[str, Any], dict[str, Any]]:
+        """OpenRouter passes the full reasoning_config dict as extra_body.reasoning."""
+        extra_body: dict[str, Any] = {}
+        if supports_reasoning:
+            if reasoning_config is not None:
+                extra_body["reasoning"] = dict(reasoning_config)
+            else:
+                extra_body["reasoning"] = {"enabled": True, "effort": "medium"}
+        return extra_body, {}
+
+
+openrouter = OpenRouterProfile(
+    name="openrouter",
+    aliases=("or",),
+    env_vars=("OPENROUTER_API_KEY",),
+    display_name="OpenRouter",
+    description="OpenRouter — unified API for 200+ models",
+    signup_url="https://openrouter.ai/keys",
+    base_url="https://openrouter.ai/api/v1",
+    models_url="https://openrouter.ai/api/v1/models",
+    fallback_models=(
+        "anthropic/claude-sonnet-4.6",
+        "openai/gpt-5.4",
+        "deepseek/deepseek-chat",
+        "google/gemini-3-flash-preview",
+        "qwen/qwen3-plus",
+    ),
+)
+
+register_provider(openrouter)