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

apps/backend/test/session-auth.test.ts

@@ -1,18 +1,20 @@
+import { beforeEach, describe, expect, it, mock, vi } from 'bun:test';
 import { Hono } from 'hono';
-import { beforeEach, describe, expect, it, vi } from 'vitest';
 
-vi.mock('@/lib/prisma', () => ({
-  default: {
-    $queryRaw: vi.fn(),
-  },
-  getPrismaClient: vi.fn(),
+const db = {
+  $queryRaw: mock(),
+};
+
+mock.module('@/lib/prisma', () => ({
+  default: db,
+  getPrismaClient: mock(() => db),
   UnitOfWork: class {},
 }));
 
-vi.mock('@/modules/auth/auth', () => ({
+mock.module('@/modules/auth/auth', () => ({
   auth: {
     api: {
-      getSession: vi.fn(),
+      getSession: mock(),
     },
   },
 }));
@@ -48,7 +50,7 @@ describe('session auth', () => {
   });
 
   it('rejects protected requests without a session', async () => {
-    vi.mocked(auth.api.getSession).mockResolvedValue(null);
+    auth.api.getSession.mockResolvedValue(null);
 
     const app = new Hono();
     app.use('*', sessionAuthMiddleware);
@@ -65,7 +67,7 @@ describe('session auth', () => {
       user: { id: 'user-1', name: 'Ana' },
       session: { id: 'session-1' },
     };
-    vi.mocked(auth.api.getSession).mockResolvedValue(session as never);
+    auth.api.getSession.mockResolvedValue(session as never);
 
     const app = new Hono();
     app.use('*', sessionAuthMiddleware);