[UX] oclite: Live subagent status panel

[randomm]

Description

Show a live panel of running subagents/tasks with their current status.

Target UX (realistic based on available data)

├── explore: running · started 15s ago
├── developer: running · started 8s ago  
└── adversarial: completed · 23s

Available Data

• Session.listBackgroundTasks() → pending task IDs + completed results
• BackgroundTaskResult → id, status (running/completed/failed), time.started, time.completed, metadata.agent_type, metadata.description
• Session.BackgroundTaskEvent.Completed/Failed → Bus events when tasks finish

NOT Available (cannot show)

• ❌ Real-time tool use count for running tasks
• ❌ Real-time token count for running tasks
• ❌ 'Thinking/Deciphering' status text for running tasks
• These would require new Bus events from subagent sessions

Requirements

• Tree-style display with connectors
• Show agent type + status + elapsed time
• Update when tasks complete/fail (via Bus events)
• Toggle visibility with ctrl+t

Files

• packages/opencode/src/cli/lite/index.ts — rendering
• packages/opencode/src/session/index.ts — task data

[randomm]

Blocked: Live subagent status panel requires a fixed panel, which we've decided against per #76 research. Will need to be reimagined as inline status output instead. Depends on #73, #74.

[randomm]

Consolidated into new issue. Partially addressed by #95 (nested child tool for running tasks). Remaining work: tree-style multi-agent panel, ctrl+t toggle.