chore: switch to @types/bun

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: stephendolan

bun.lock

@@ -1,6 +1,6 @@
 {
   "name": "@stephendolan/ynab-cli",
-  "version": "2.2.0",
+  "version": "2.3.0",
   "description": "A command-line interface for You Need a Budget (YNAB)",
   "type": "module",
   "main": "./dist/cli.js",
@@ -55,7 +55,7 @@
   },
   "devDependencies": {
     "@biomejs/biome": "^1.9.4",
-    "@types/node": "^20.0.0",
+    "@types/bun": "latest",
     "oxlint": "^0.16.0",
     "tsup": "^8.0.0",
     "tsx": "^4.7.0",