fix(plugins): register dynamically-loaded modules in sys.modules before exec

Dashboard plugin API routes (web_server._mount_plugin_api_routes) and
gateway event hooks (gateway.hooks.HookRegistry.discover_and_load) both
loaded Python files via importlib.util.spec_from_file_location +
exec_module without registering the resulting module in sys.modules.

That breaks any plugin or hook handler that uses `from __future__ import
annotations` together with a Pydantic BaseModel / dataclass / anything
that introspects `__module__`: at first request Pydantic tries to
resolve string-form type hints against the defining module's namespace,
can't find it by name, and raises:

  PydanticUserError: TypeAdapter[...] is not fully defined;
  you should define ... and all referenced types,
  then call `.rebuild()` on the instance.

This is what broke the kanban dashboard's 'triage' button — POST
/api/plugins/kanban/tasks validated against CreateTaskBody (a Pydantic
model in a file using `from __future__ import annotations`) and
returned 500 on every click.

The fix, applied symmetrically to both loaders:

  1. Compute module_name once.
  2. Register the module in sys.modules BEFORE exec_module.
  3. On exec_module failure, pop the half-initialized stub so subsequent
     reloads don't pick up broken state.

GETs were unaffected because they don't build a body TypeAdapter, which
is why this only surfaced when users started POSTing.

hermes_cli/web_server.py

@@ -3224,13 +3224,23 @@ def _mount_plugin_api_routes():
             _log.warning("Plugin %s declares api=%s but file not found", plugin["name"], api_file_name)
             continue
         try:
-            spec = importlib.util.spec_from_file_location(
-                f"hermes_dashboard_plugin_{plugin['name']}", api_path,
-            )
+            module_name = f"hermes_dashboard_plugin_{plugin['name']}"
+            spec = importlib.util.spec_from_file_location(module_name, api_path)
             if spec is None or spec.loader is None:
                 continue
             mod = importlib.util.module_from_spec(spec)
-            spec.loader.exec_module(mod)
+            # Register in sys.modules BEFORE exec_module so pydantic/FastAPI
+            # can resolve forward references (e.g. models defined in a file
+            # that uses `from __future__ import annotations`). Without this,
+            # TypeAdapter lazy-build fails at first request with
+            # "is not fully defined" because the module namespace isn't
+            # reachable by name for string-annotation resolution.
+            sys.modules[module_name] = mod
+            try:
+                spec.loader.exec_module(mod)
+            except Exception:
+                sys.modules.pop(module_name, None)
+                raise
             router = getattr(mod, "router", None)
             if router is None:
                 _log.warning("Plugin %s api file has no 'router' attribute", plugin["name"])