fix: discover plugins before reading plugin toolsets in tools_config (#3457)

hermes tools and _get_platform_tools() call get_plugin_toolsets() /
_get_plugin_toolset_keys() without first ensuring plugins have been
discovered. discover_plugins() only runs as a side effect of importing
model_tools.py, which hermes tools never does. This means:

- hermes tools TUI never shows plugin toolsets (invisible to users)
- _get_platform_tools() in standalone processes misses plugin toolsets

Fix: call discover_plugins() (idempotent) in both
_get_plugin_toolset_keys() and _get_effective_configurable_toolsets()
before accessing plugin state. In the gateway/CLI where model_tools.py
is already imported, the call is a no-op (discover_and_load checks
_discovered flag).

hermes_cli/tools_config.py

@@ -108,7 +108,8 @@ def _get_effective_configurable_toolsets():
     """
     result = list(CONFIGURABLE_TOOLSETS)
     try:
-        from hermes_cli.plugins import get_plugin_toolsets
+        from hermes_cli.plugins import discover_plugins, get_plugin_toolsets
+        discover_plugins()  # idempotent — ensures plugins are loaded
         result.extend(get_plugin_toolsets())
     except Exception:
         pass
@@ -118,7 +119,8 @@ def _get_effective_configurable_toolsets():
 def _get_plugin_toolset_keys() -> set:
     """Return the set of toolset keys provided by plugins."""
     try:
-        from hermes_cli.plugins import get_plugin_toolsets
+        from hermes_cli.plugins import discover_plugins, get_plugin_toolsets
+        discover_plugins()  # idempotent — ensures plugins are loaded
         return {ts_key for ts_key, _, _ in get_plugin_toolsets()}
     except Exception:
         return set()