chore(tooling): migrate from Biome to ESLint + Prettier

Replace Biome lint/check/format scripts with ESLint and Prettier commands, add Next + TypeScript oriented ESLint flat config, and remove biome.json. Update dependencies and lockfile to a single lint stack with Prettier-based formatting.

package.json

@@ -6,10 +6,11 @@
     "dev": "next dev --turbopack",
     "build": "next build",
     "start": "next start",
-    "lint": "biome check .",
-    "lint:fix": "biome check --write .",
-    "format": "biome format --write .",
-    "check": "biome ci .",
+    "lint": "eslint . --max-warnings=0",
+    "lint:fix": "eslint . --fix",
+    "format": "prettier \"**/*.{ts,tsx,js,jsx,mjs,cjs,json,css,yml,yaml}\" --write",
+    "format:check": "prettier \"**/*.{ts,tsx,js,jsx,mjs,cjs,json,css,yml,yaml}\" --check",
+    "check": "pnpm lint && pnpm typecheck && pnpm format:check",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
@@ -31,11 +32,17 @@
     "zustand": "^5.0.11"
   },
   "devDependencies": {
-    "@biomejs/biome": "^2.4.3",
     "@tailwindcss/postcss": "^4",
+    "@typescript-eslint/eslint-plugin": "^8.56.0",
+    "@typescript-eslint/parser": "^8.56.0",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "eslint": "^9.39.3",
+    "eslint-config-next": "^16.1.6",
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-react-hooks": "^7.0.1",
+    "prettier": "^3.8.1",
     "shadcn": "^3.8.5",
     "tailwindcss": "^4",
     "tw-animate-css": "^1.4.0",