Ghost sub-agent delegations stuck as 'running' in sidebar after completion/restart

Description

Background sub-agent delegations that complete (or time out) continue to appear as "running" in the sidebar TUI even after:

1. Restarting the app
2. Killing all opencode processes (kill -9)
3. Full macOS restart

The ghost entries are stuck in the "running" state indefinitely. Observed with jd-judge-* delegations that completed with "no assistant response" but stayed as "running" for hours.

Reproduction

1. Launch a sub-agent delegation
2. Let it complete or time out
3. Restart opencode
4. Delegation reappears as "running" in the sidebar (stale state)

Expected Behavior

Completed/timeout delegations should be removed from the sidebar after restart, or show their actual terminal state.

Suggested Enhancement: Manual Delegation Dismissal

Since the sidebar already supports mouse interaction (clicking on delegations, switching between them), add the ability for the user to manually close/dismiss a delegation entry from the sidebar. This would serve as both a workaround for stuck ghost entries and a general UX improvement.

Options:

• Right-click context menu on a delegation → "Close" / "Dismiss"
• Hover + (X) button on each delegation row
• Keyboard shortcut on selected delegation (e.g. Ctrl+W or Delete)

Environment

• Opencode 1.18.11 (Homebrew)
• macOS Apple Silicon
• Plugin: opencode-subagent-statusline v1.2.1