Migrate API to Elysia and switch runtime to Bun

package.json

@@ -2,17 +2,19 @@
   "name": "fiscal-frontend",
   "version": "2.0.0",
   "private": true,
+  "packageManager": "bun@1.3.5",
   "scripts": {
-    "dev": "next dev --turbopack",
-    "build": "next build --turbopack",
-    "start": "next start",
-    "lint": "next lint"
+    "dev": "bun --bun next dev --turbopack",
+    "build": "bun --bun next build --turbopack",
+    "start": "bun --bun next start",
+    "lint": "bun --bun tsc --noEmit"
   },
   "dependencies": {
     "@tailwindcss/postcss": "^4.2.1",
     "better-auth": "^1.4.19",
     "clsx": "^2.1.1",
     "date-fns": "^4.1.0",
+    "elysia": "latest",
     "lucide-react": "^0.575.0",
     "next": "^16.1.6",
     "pg": "^8.18.0",