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>

backend/app/core/settings_registry.py

@@ -275,6 +275,16 @@ register_setting(SettingDefinition(
     category="modules"
 ))
 
+register_setting(SettingDefinition(
+    key="modules_order",
+    type=SettingType.LIST,
+    scope=SettingScope.GLOBAL,
+    storage=SettingStorage.DATABASE,
+    default=["feature1", "feature2", "feature3"],
+    description="Order of feature modules in sidebar",
+    category="modules"
+))
+
 
 # =============================================================================
 # AUTHENTICATION & SECURITY SETTINGS (Global, Database)