Deployment cancellation is claimed but not implemented

[Alimedhat000]

Summary

The worker has no per-job cancellation and no debounce. Once a deployment job starts, it cannot be aborted, and a new deploy to the same app does not supersede an in-flight one.

Evidence

• Worker is a single BullMQ worker with concurrency 1 (packages/worker/src/index.ts).
• No cancel/abort/debounce logic in worker/src/deployments/ or api/src/routes/deployments.ts.

Scope

• Abort an in-flight build (kill build/exec container, best-effort) and mark the deployment cancelled.
• Surface cancellation in the web UI.
• Auto "latest-wins" debounce on new deploys for the same app is tracked separately in latest-wins cancellation — cancel running deployment when new one arrives #35. This issue covers the general cancellation mechanism (user-initiated cancel + worker abort) that latest-wins cancellation — cancel running deployment when new one arrives #35 assumes.