feat: add PostgreSQL persistence for permanent shareable links

- Add PostgreSQL service to docker-compose with health checks
- Add migrate service that runs prisma migrate deploy on startup
- Integrate Prisma client in worker: checks for existing generations
  (same repo+commit) before regenerating, writes to Postgres on completion
- Update /api/docs/[id] with Redis → PostgreSQL fallback + cache repopulation
- Update Dockerfile: prisma generate in build, copy Prisma engine to worker/web
- Add @codeboard/database dependency to web and worker packages
- Add initial SQL migration for Generation and User tables
- Change removeOnComplete to { age: 3600 } for job retention

apps/worker/package.json

@@ -13,6 +13,7 @@
     "@codeboard/parser": "*",
     "@codeboard/llm": "*",
     "@codeboard/diagrams": "*",
+    "@codeboard/database": "*",
     "bullmq": "^5.34.0",
     "ioredis": "^5.4.0",
     "simple-git": "^3.27.0"