refactor: migrate monorepo from pnpm to Bun runtime and workspaces

- root: bun workspaces via package.json, packageManager bun@1.4.0, scripts use bun --filter
- backend: Bun.serve, bun test (vitest removed), bun --watch dev script, tsconfig types bun
- tests: migrate 6 test files from vitest to bun:test (mock.module)
- validate: replace @hono/zod-validator with hono validator + zod safeParse (fixes TS2589)
- lockfile: bunfig.toml saveTextLockfile, regenerated bun.lock (text) for turbo
- docs: AGENTS.md, README.md, stack.md updated to Bun stack

package.json

@@ -3,23 +3,27 @@
   "version": "0.1.0",
   "private": true,
   "type": "module",
+  "workspaces": [
+    "apps/*",
+    "packages/*"
+  ],
   "scripts": {
     "dev": "turbo dev",
     "build": "turbo build",
     "lint": "turbo lint",
     "lint:fix": "turbo lint:fix",
     "typecheck": "turbo typecheck",
-    "test": "pnpm --filter @gruperly/backend test",
-    "db:generate": "pnpm --filter @gruperly/backend db:generate",
-    "db:migrate": "pnpm --filter @gruperly/backend db:migrate",
-    "db:push": "pnpm --filter @gruperly/backend db:push",
-    "db:studio": "pnpm --filter @gruperly/backend db:studio"
+    "test": "bun --filter @gruperly/backend test",
+    "db:generate": "bun --filter @gruperly/backend db:generate",
+    "db:migrate": "bun --filter @gruperly/backend db:migrate",
+    "db:push": "bun --filter @gruperly/backend db:push",
+    "db:studio": "bun --filter @gruperly/backend db:studio"
   },
   "devDependencies": {
     "@biomejs/biome": "^2.4.15",
     "turbo": "^2.3.3"
   },
-  "packageManager": "pnpm@9.0.0",
+  "packageManager": "bun@1.4.0",
   "engines": {
     "node": ">=20"
   }