feat: show update available when catalog version differs from installed

Catalog partial now compares catalog version vs installed plugin.yaml version.
Gold border + "Update available — installed vX.Y.Z" badge when newer.
Update button uses btn-warn styling. Route passes installed_versions dict.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fabledscryer/settings/routes.py

@@ -256,11 +256,13 @@ async def plugins_catalog():
 
     discovered = _discover_plugins()
     installed_names = {p["_dir"] for p in discovered}
+    installed_versions = {p["_dir"]: p.get("version", "0.0.0") for p in discovered}
 
     return await render_template(
         "settings/_catalog_partial.html",
         catalog=catalog,
         installed_names=installed_names,
+        installed_versions=installed_versions,
         loaded_names=_LOADED_PLUGINS,
         error=error,
     )