Upgrade to Next.js 16.1.6, React 19.2.4, and update all dependencies

- Next.js 15.5 → 16.1.6 (Turbopack default, faster builds)
- React/React-DOM 19.1 → 19.2.4
- @types/react 18 → 19, @types/react-dom 18 → 19
- TypeScript 5.2 → 5.9
- CI Node.js 18 → 20 (required by Next.js 16)
- Replace removed next lint with standalone ESLint config
- Auto-updated tsconfig.json (jsx: react-jsx, dev types)

package.json

@@ -6,7 +6,7 @@
     "dev": "./scripts/kill-dev.sh && next dev",
     "build": "next build",
     "start": "next start",
-    "lint": "next lint",
+    "lint": "eslint . --ext .ts,.tsx --ignore-path .gitignore",
     "test": "jest",
     "test:watch": "jest --watch",
     "security:check": "node scripts/security/security-check.js",
@@ -20,31 +20,31 @@
     "axios": "^1.6.2",
     "bcryptjs": "^3.0.2",
     "cheerio": "^1.1.0",
-    "next": "^15.3.4",
+    "next": "^16.1.6",
     "pg": "^8.16.2",
-    "react": "^19.1.0",
-    "react-dom": "^19.1.0"
+    "react": "^19.2.4",
+    "react-dom": "^19.2.4"
   },
   "devDependencies": {
-    "@testing-library/jest-dom": "^6.6.3",
-    "@testing-library/react": "^16.3.0",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
     "@types/jest": "^30.0.0",
-    "@types/react": "^18.2.43",
-    "@types/react-dom": "^18.2.17",
+    "@types/react": "^19.2.14",
+    "@types/react-dom": "^19.2.3",
     "@typescript-eslint/eslint-plugin": "^6.14.0",
     "@typescript-eslint/parser": "^6.14.0",
     "@vitejs/plugin-react": "^4.2.1",
-    "autoprefixer": "^10.4.16",
+    "autoprefixer": "^10.4.24",
     "eslint": "^8.55.0",
     "eslint-plugin-react-hooks": "^4.6.0",
     "eslint-plugin-react-refresh": "^0.4.5",
     "husky": "^9.1.7",
     "jest": "^30.0.0",
     "jest-environment-jsdom": "^30.0.0",
-    "postcss": "^8.4.32",
+    "postcss": "^8.5.6",
     "tailwindcss": "^3.3.0",
-    "tsx": "^4.20.3",
-    "typescript": "^5.2.2",
+    "tsx": "^4.21.0",
+    "typescript": "^5.9.3",
     "vite": "^5.0.8"
   }
 }