Implement plugin dynamic settings routes architecture

Plugins can now register their settings pages dynamically via get_settings_routes()
hook, eliminating hardcoded imports that break lean builds.

Backend:
- Add get_settings_routes() hook to BasePlugin (shopdb/plugins/base.py)
- Implement in ComputersPlugin for Operating Systems management
- Add /api/plugins/settings-routes endpoint to expose plugin routes

Frontend:
- ModelCatalogHub fetches plugin routes and dynamically adds them via router.addRoute()
- Tabs render dynamically from pluginTabs ref
- Components lazy-load when clicked

Benefits:
- Lean builds work without manual route exclusions
- Plugins self-contain their UI extensions
- No core code changes needed when adding plugin settings pages
- Follows plugin architecture best practices

Fixes TODO from commit a03fd3de4f

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

shopdb/core/api/plugins.py

@@ -42,6 +42,30 @@ def list_enabled_plugins():
     return success_response(sorted(names))
 
 
+@plugins_bp.route('/settings-routes', methods=['GET'])
+@jwt_required(optional=True)
+def get_plugin_settings_routes():
+    """Return settings routes contributed by all enabled plugins.
+
+    Plugins can register routes to add tabs/pages to settings hubs like
+    Model Catalog, Asset Config, etc. Frontend router merges these dynamically.
+
+    Returns: { routes: [{hub, path, name, tab, component}, ...] }
+    """
+    pm = current_app.extensions.get('plugin_manager')
+    if not pm:
+        return success_response({'routes': []})
+
+    routes = []
+    for plugin in pm.get_enabled_plugin_instances():
+        if hasattr(plugin, 'get_settings_routes'):
+            plugin_routes = plugin.get_settings_routes()
+            if plugin_routes:
+                routes.extend(plugin_routes)
+
+    return success_response({'routes': routes})
+
+
 @plugins_bp.route('/<name>', methods=['PUT'])
 @jwt_required()
 @require_role('admin')