Add budget-allocator-server example

Demo MCP App for interactive budget allocation with:
- Slider controls for 5 categories (Marketing, Engineering, etc.)
- Real-time donut chart visualization via Chart.js
- 24-month sparkline trends per category
- Industry benchmark percentile badges
- Company stage selector (Seed through Growth)
- Budget preset buttons ($50K-$500K)

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

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

package-lock.json

@@ -109,6 +109,26 @@
         "vite-plugin-singlefile": "^2.3.0"
       }
     },
+    "examples/budget-allocator-server": {
+      "version": "1.0.0",
+      "dependencies": {
+        "@modelcontextprotocol/ext-apps": "../..",
+        "@modelcontextprotocol/sdk": "^1.22.0",
+        "chart.js": "^4.4.0",
+        "zod": "^3.25.0"
+      },
+      "devDependencies": {
+        "@types/cors": "^2.8.19",
+        "@types/express": "^5.0.0",
+        "@types/node": "^22.0.0",
+        "concurrently": "^9.2.1",
+        "cors": "^2.8.5",
+        "express": "^5.1.0",
+        "typescript": "^5.9.3",
+        "vite": "^6.0.0",
+        "vite-plugin-singlefile": "^2.3.0"
+      }
+    },
     "examples/cohort-heatmap-server": {
       "version": "1.0.0",
       "dependencies": {
@@ -1211,6 +1231,10 @@
         "node": "^6 || ^7 || ^8 || ^9 || ^10 || ^11 || ^12 || >=13.7"
       }
     },
+    "node_modules/budget-allocator-server": {
+      "resolved": "examples/budget-allocator-server",
+      "link": true
+    },
     "node_modules/bun": {
       "version": "1.3.3",
       "cpu": [