fix: teardown UI sibling gracefully on ok start exit

[Adityakk9031]

Resolves #692

Description

This PR fixes an issue where stopping the server (ok start) via Ctrl+C would leave a detached, stale ok ui process running in the background, which locked up the port.

Previously, when a user interrupted the ok start command, the CLI correctly tore down the backend services but did not signal the sibling ok ui process (which runs detached). The UI process would persist in the background until its 12-hour safety timer expired.

What Changed

• Extracted Teardown Logic: The UI teardown procedure—previously isolated inside the server's idle timeout handler (buildIdleShutdownHandler)—was extracted into a reusable teardownUiSibling helper.
• Wired into System Shutdown: Hooked teardownUiSibling into the standard SIGINT and SIGTERM shutdown handlers within runStartCommand.
• Now, when you shut down the primary server, the parent explicitly reads the lockfile, sends a SIGTERM to the sibling UI process, waits gracefully for it to exit, and escalates to SIGKILL if it gets stuck.

Testing

• Confirmed that pressing Ctrl+C during ok start --open now correctly kills both the collab server and the proxying UI process.
• Changeset included for automated release notes.

[CLAassistant]

All committers have signed the CLA.

[Adityakk9031]

@tim-inkeep have a look

[github-actions]

I could not sync this PR automatically. A maintainer will look into it.

The diff could not be applied on our side. This is a bridge-side issue, not a problem with your PR (which is already based on the latest public base); a maintainer will look into it.

Falling back to direct application...
error: cannot apply binary patch to 'public/open-knowledge/.changeset/stale-ui-shutdown.md' without full index line
error: public/open-knowledge/.changeset/stale-ui-shutdown.md: patch does not apply
Applied patch to 'public/open-knowledge/packages/cli/src/commands/start.ts' cleanly.