fix(db): add build script to generate Prisma client for CI

- Add build script that runs 'prisma generate'
- Ensures Prisma client is generated during CI build phase
- Fixes type-check failures caused by missing PrismaClient type

This resolves CI errors:
- error TS2305: Module '"@prisma/client"' has no exported member 'PrismaClient'

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

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

packages/db/package.json

@@ -6,6 +6,7 @@
   "main": "./src/index.ts",
   "types": "./src/index.ts",
   "scripts": {
+    "build": "prisma generate",
     "db:generate": "prisma generate",
     "db:push": "prisma db push",
     "db:migrate": "prisma migrate dev",