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.

docker-compose.yml

@@ -7,6 +7,8 @@ services:
       POSTGRES_DB: ${POSTGRES_DB}
     volumes:
       - postgres-data:/var/lib/postgresql/data
+    ports:
+      - "5432:5432"
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
       interval: 5s