PM-5846: apply database migrations before API startup

[jmgasper]

What was broken

Closed ticket owners received a 500 Internal Server Error when submitting a reply, while replies to open tickets continued to work.

Root cause

The deployed reopen path writes notification outbox rows with the TICKET_REOPENED PostgreSQL enum value. That value is introduced by a Prisma migration, but the production container started the API directly and depended on a manual one-off migration. When application code was deployed ahead of the database migration, PostgreSQL rejected the reopen transaction and Nest returned a generic 500.

What was changed

• Added a production startup script that runs prisma migrate deploy before starting the API.
• Made startup fail safely if a pending migration cannot be applied.
• Updated the Docker image to invoke the migration-aware startup script.
• Updated deployment documentation to describe automatic migrations and concurrent-task safety.

Any added/updated tests

• Added startup regression coverage verifying the production image invokes the startup script.
• Verified migrations run before Node starts.
• Verified a migration failure prevents the API from starting.
• Ran the full test suite: 51 tests passed.
• Ran pnpm lint, pnpm build, sh -n appStartUp.sh, git diff --check, and docker build --check . successfully.

A full Docker image build was also attempted twice, but both attempts stopped in the pre-existing Alpine package-install layer because dl-cdn.alpinelinux.org returned transient DNS errors. No changed Docker layer failed.