Add graceful shutdown that cleans up DB and jobs

[robertocarlous]

Body:

The process should respond to SIGTERM/SIGINT by stopping new requests, waiting for in-flight requests to finish, shutting down cron jobs, and disconnecting Prisma clients.

Acceptance Criteria:

• Server stops accepting new requests on SIGTERM.
• In-flight requests are given a configurable grace period to finish.
• Prisma disconnect is called before process exit.

[dotunv]

I am very interested in solving this issue

[grantfox-oss]

🦊 GrantFox — @dotunv has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #149)
2. Your PR will be reviewed by the Neurowealth maintainers

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