## Why
Stream animation ticks generated on a background thread can accumulate while the
TUI is busy, causing stale ticks to run after the animation stops or the chat
widget is replaced.
## What changed
- Replace the animation thread and `CommitTick` app event with a Tokio interval
owned by the foreground event loop.
- Delay missed ticks instead of replaying a burst, and let pending app events run
before animation work.
- Drop the interval when animation stops or the chat widget is replaced, while
preserving `CommitTick` session-log entries.
## Testing
Add a paused-time test covering stable pacing, missed ticks, restart behavior,
and chat-widget replacement.
GitOrigin-RevId: d0561d3f8962b5e05a728463e76aa8ec83cd5a31
Tamir Duberstein
a95391160a