[UX] Subagent task progress: nested status line + elapsed time

[randomm]

Problem

When the PM dispatches a subagent task (e.g., @git-agent), the user only sees:

◆ task  @git-agent: Get current git and project state

There's no visibility into:

1. What the subagent is currently doing (which tool is running)
2. How long the task has been running

This makes it hard to understand at a glance what's happening — especially when multiple subagents are working.

Proposed Solution

Show a nested status line below each running subagent task:

✓ bash  remory search "architecture stack"
✓ read  ratcher/README.md
◆ task  @git-agent: Get current git state (12s)
    └─ ◇ bash  git log --oneline -5
✓ bash  remory add "Ratcher workflow..."

Features:

1. Elapsed time ticker — (12s) updates live showing task duration
2. Nested current tool — indented line showing what tool the subagent is currently running
3. Visual hierarchy — clear distinction between PM's direct tools vs delegated subagent work
4. Live updates — the nested line updates as subagent progresses through tools

When subagent completes:

✓ task  @git-agent: Get current git state (45s)

The nested line disappears, elapsed time freezes at completion time.

Technical Considerations

• Need to subscribe to child session's tool events
• The panel.ts already tracks child sessions — could reuse that
• The liveblock.ts renders tools — needs to support nested/hierarchical display
• Elapsed time requires a timer interval (already have 80ms render loop)

Related Issues

• [UX] oclite: Live subagent status panel #68 — Live subagent status panel
• [UI] Live Task Status Panel #19 — Live Task Status Panel
• feat: Subagent output panel with Ctrl+X navigation #88 — Subagent output panel (Ctrl+X navigation)

Acceptance Criteria

• Running subagent tasks show elapsed time ticker
• Running subagent tasks show nested current tool status
• Nested status updates live as subagent progresses
• Clear visual hierarchy between direct tools and delegated tasks
• Completed tasks show final elapsed time (no nested line)

[randomm]

Implemented in ce74e69: Tasks now show elapsed time ticker and nested child tool status