fix(frontend): downgrade to stable React 18 & Next.js 15 to resolve CI build error

The CI workflow was failing with 'Cannot read properties of undefined (reading ReactCurrentBatchConfig)' error.

Root cause: Next.js 16.1.6 (unstable) with React 19 caused compatibility issues.

Fix:
- Downgraded Next.js from 16.1.6 → 15.1.6 (stable)
- Downgraded React from 19.2.3 → 18.3.1 (stable with Next.js 15)
- Downgraded React-DOM from 19.2.3 → 18.3.1 (to match React version)

This should resolve all 3 CI build failures (#14, #15, #16).

Author: DHANUSHGCODE

frontend/package.json

@@ -10,9 +10,9 @@
   },
   "dependencies": {
     "lucide-react": "^0.563.0",
-    "next": "16.1.6",
-    "react": "19.2.3",
-    "react-dom": "19.2.3",
+    "next": "15.1.6",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1",
     "recharts": "^3.7.0",
     "three": "^0.160.0",
     "@react-three/fiber": "^8.15.0",