Code Link: Ensure the server stops reliably with --once

[iamakulov]

I ran into npx framer-code-link --once hanging after printing

$ npx framer-code-link --once --dir .

  ⚡ Code Link v0.21.0

  Waiting for Plugin connection...
✓ Connected to 💙 Shaders 2026
✓ Synced into . (0 files updated, 29 unchanged)
  Sync complete, exiting...

This usually happens because we forgot to clean up something (timeouts or sockets). But it’s easy to forget to clean things up, so process.exit() should fix it for good.

[Copilot]

Pull request overview

This PR improves shutdown behavior for the Code Link CLI, specifically aiming to make --once runs terminate reliably by cleaning up pending dependency-version timeouts during shutdown and force-exiting after watcher/server teardown.

Changes:

• Clear any pending dependency-version request timeout during shutdown.
• In --once mode, explicitly process.exit(0) after closing the watcher and WebSocket server.

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[huntercaron]

LGTM!