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/prisma/migrations/migration_lock.toml

@@ -0,0 +1,3 @@
+# Please do not edit this file manually
+# It should be added in your version-control system (e.g., Git)
+provider = "postgresql"