fix(web): clean up remaining Next.js artifacts in Vite migration

- Add vite-env.d.ts for import.meta.env and asset type declarations
- Remove dead layout.tsx (providers already in main.tsx)
- Fix useSearchParams destructuring to [searchParams] tuple (11 locations)
- Replace process.env.NEXT_PUBLIC_* with import.meta.env.VITE_*
- Fix langbotIcon.src to langbotIcon (Vite returns URL string)
- Fix Link href to Link to for react-router-dom
- Fix navigate({ scroll: false }) to { preventScrollReset: true }
- Fix [router] dependency arrays to [navigate]
- Remove Next.js plugin from tsconfig, set rsc: false in components.json
- Replace next lint with eslint in lint-staged

web/package.json

@@ -11,7 +11,7 @@
   },
   "lint-staged": {
     "*.{js,jsx,ts,tsx}": [
-      "next lint --fix",
+      "eslint --fix",
       "prettier --write"
     ]
   },