chore: opportunistically clean up containers for completed tasks

[ereslibre]

Adds opportunistic container cleanup across the CLI so that containers for tasks in terminal states are automatically removed, freeing up resources without requiring an explicit user action.

Task output is already persisted via mounted volumes, so removing the container is safe. FAILED tasks are intentionally kept so users can still debug the container.

Changes

• Added tryRemoveTaskContainer() helper in packages/cli/src/lib/sandbox/index.ts — a best-effort function that stops and removes a task's container and clears its container metadata
• Added isTerminalStatus() and isActiveStatus() utilities in packages/cli/src/utils/task-status.ts to classify task states
• list command: opportunistically removes containers when a task reaches a terminal status (COMPLETED, MERGED, PUSHED)
• iterate command: removes the previous iteration's container before starting a new one
• restart command: removes the previous container before starting a new one
• cleanup command: bulk-removes containers for all non-active tasks during cleanup

Notes

The cleanup in the list command is fire-and-forget (.catch(() => {})), while iterate and restart await the removal since they need the container gone before starting a new one. The cleanup command also awaits removal but wraps each attempt in a try/catch for best-effort semantics.

[Angelmmiguel]

LGTM! Added a comment before approving.