feat: add Request and Job schema with migration

Adds the Prisma schema (Request/Job models, RequestStatus/JobState
enums), a Prisma client singleton at web/src/lib/db.ts, and the
init_request_job migration, applied and verified against Postgres.

Also publishes the db service's port (5432:5432) in docker-compose.yml
so host-run Prisma commands can reach localhost:5432 for local dev.

web/package.json

@@ -6,7 +6,10 @@
     "dev": "next dev",
     "build": "next build",
     "start": "next start",
-    "test": "vitest run"
+    "test": "vitest run",
+    "postinstall": "prisma generate",
+    "db:migrate": "prisma migrate deploy",
+    "db:dev": "prisma migrate dev"
   },
   "dependencies": {
     "next": "15.5.20",