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/qwen-oauth/__init__.py

@@ -0,0 +1,82 @@
+"""Qwen Portal provider profile."""
+
+import copy
+from typing import Any
+
+from providers import register_provider
+from providers.base import ProviderProfile
+
+
+class QwenProfile(ProviderProfile):
+    """Qwen Portal — message normalization, vl_high_resolution, metadata top-level."""
+
+    def prepare_messages(self, messages: list[dict[str, Any]]) -> list[dict[str, Any]]:
+        """Normalize content to list-of-dicts format.
+
+        Inject cache_control on system message.
+
+        Matches the behavior of run_agent.py:_qwen_prepare_chat_messages().
+        """
+        prepared = copy.deepcopy(messages)
+        if not prepared:
+            return prepared
+
+        for msg in prepared:
+            if not isinstance(msg, dict):
+                continue
+            content = msg.get("content")
+            if isinstance(content, str):
+                msg["content"] = [{"type": "text", "text": content}]
+            elif isinstance(content, list):
+                normalized_parts = []
+                for part in content:
+                    if isinstance(part, str):
+                        normalized_parts.append({"type": "text", "text": part})
+                    elif isinstance(part, dict):
+                        normalized_parts.append(part)
+                if normalized_parts:
+                    msg["content"] = normalized_parts
+
+        # Inject cache_control on the last part of the system message.
+        for msg in prepared:
+            if isinstance(msg, dict) and msg.get("role") == "system":
+                content = msg.get("content")
+                if (
+                    isinstance(content, list)
+                    and content
+                    and isinstance(content[-1], dict)
+                ):
+                    content[-1]["cache_control"] = {"type": "ephemeral"}
+                break
+
+        return prepared
+
+    def build_extra_body(
+        self, *, session_id: str | None = None, **context
+    ) -> dict[str, Any]:
+        return {"vl_high_resolution_images": True}
+
+    def build_api_kwargs_extras(
+        self,
+        *,
+        reasoning_config: dict | None = None,
+        qwen_session_metadata: dict | None = None,
+        **context,
+    ) -> tuple[dict[str, Any], dict[str, Any]]:
+        """Qwen metadata goes to top-level api_kwargs, not extra_body."""
+        top_level = {}
+        if qwen_session_metadata:
+            top_level["metadata"] = qwen_session_metadata
+        return {}, top_level
+
+
+qwen = QwenProfile(
+    name="qwen-oauth",
+    aliases=("qwen", "qwen-portal", "qwen-cli"),
+    env_vars=("QWEN_API_KEY",),
+    base_url="https://portal.qwen.ai/v1",
+    auth_type="oauth_external",
+    default_max_tokens=65536,
+)
+
+register_provider(qwen)

plugins/model-providers/qwen-oauth/plugin.yaml

@@ -0,0 +1,5 @@
+name: qwen-oauth-provider
+kind: model-provider
+version: 1.0.0
+description: Qwen Portal (OAuth)
+author: Nous Research