fix: animate spinner in foreground and async subagent widgets

[NOirBRight]

Problem

The spinner (running glyph) in both foreground subagent results and async widget frequently freezes during long-running subagent tasks — especially when the child agent is waiting for LLM responses with no status file updates.

Root Cause

1. No animation driver: The spinner glyph was computed from static state values (seed = sum of toolCount/durationMs/etc). When the subagent went idle waiting for LLM, none of these values changed, so the rendered glyph stayed frozen on the same frame.
2. Static component tree: created a of nodes at render time. The text content was baked in and never refreshed unless changed (which only happens on status file updates).
3. Missing foreground timer: The foreground had no mechanism to trigger periodic re-renders while the subagent was running.

Changes

• ****: Now mixes into the seed, so the selected Braille frame rotates continuously (~8fps) even when underlying state is unchanged.
• ****: Returns a dynamic component whose callback recalculates all lines on every TUI frame, instead of pre-computing a static .
• Widget animation timer: Added / . When any async job is , a calls to keep the widget refreshing. Cleared automatically when all jobs finish.
• ****: Added to the widget component for pi-tui contract compliance.

• ****: Extracted a typed interface for the render context, replacing scattered assertions.
• ****: When the result still has running children, creates a that calls . The timer is automatically cleaned up via a hook on the returned component (called by pi-tui when the tool result is removed from the chat).

Verification

• Async widget spinner rotates smoothly during 20–30 second LLM waits.
• Foreground result spinner rotates smoothly while the child agent streams output.
• Both timers are cleaned up after the subagent completes (no leaks observed in session logs).

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[NOirBRight]

Closing in favor of #244, which carries the spinner animation fix together with the session-scoped temp directory changes currently needed by the fork.