Add module ordering feature with drag-and-drop

- Add modules_order setting in backend settings registry
- Update ModulesContext with moduleOrder state and save functions
- Create configuration tab in Features page with drag-and-drop reordering
- Make feature tabs dynamic based on order (updates in real-time)
- Sort sidebar modules based on saved order
- Add order-cards CSS with vertical layout
- Update API client to support string[] type for modules_order

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/locales/en.json

@@ -55,7 +55,11 @@
   },
   "featuresPage": {
     "title": "Features",
-    "subtitle": "Configure application features"
+    "subtitle": "Configure application features",
+    "configTab": "Configuration",
+    "orderSection": "Sidebar Order",
+    "orderDesc": "Drag to reorder features in the sidebar",
+    "applyOrder": "Apply"
   },
   "sourcesPage": {
     "title": "Sources",