feat: migrate Phase 12 components with registry updates (Phase 11 continuation)

Added 3 additional JSON component definitions and interfaces:
- ComponentTreeDemoPage: Demo page for component tree visualization
- JsonFlaskDesigner: Designer for Flask app config using JSON
- JsonStyleDesigner: Designer for styling config using JSON

Changes:
- Created 2 JSON definitions in src/components/json-definitions/
- Created 3 TypeScript interfaces in src/lib/json-ui/interfaces/
- Updated interfaces/index.ts to export all new interfaces
- Updated json-components.ts exports for all 3 new components
- Updated json-components-registry.json with 3 new entries
- Updated registry statistics: 373 → 376 total, 223 → 226 JSON-compatible

Build status: PASS ✓
All components verified and building successfully.

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

json-components-registry.json

@@ -4761,11 +4761,41 @@
       "status": "supported",
       "source": "components",
       "jsonCompatible": true
+    },
+    {
+      "type": "ComponentTreeDemoPage",
+      "name": "Component Tree Demo Page",
+      "category": "page",
+      "canHaveChildren": true,
+      "description": "Demo page for component tree visualization",
+      "status": "supported",
+      "source": "components",
+      "jsonCompatible": true
+    },
+    {
+      "type": "JsonFlaskDesigner",
+      "name": "JSON Flask Designer",
+      "category": "page",
+      "canHaveChildren": true,
+      "description": "Designer for Flask application configuration using JSON",
+      "status": "supported",
+      "source": "components",
+      "jsonCompatible": true
+    },
+    {
+      "type": "JsonStyleDesigner",
+      "name": "JSON Style Designer",
+      "category": "page",
+      "canHaveChildren": true,
+      "description": "Designer for styling configuration using JSON",
+      "status": "supported",
+      "source": "components",
+      "jsonCompatible": true
     }
   ],
   "statistics": {
-    "total": 373,
-    "jsonCompatible": 223,
+    "total": 376,
+    "jsonCompatible": 226,
     "coverage": "60%"
   }
 }