Show streaming reasoning summaries in the TUI status row

[copyberry]

Show streaming reasoning summaries in the TUI status row

What changed

• Update the status heading from the latest usable reasoning line and retain it through tool activity and empty reasoning items. Keep completed reasoning in the expanded transcript only.
• Restore active reasoning after resume, thread switches, and session refreshes, including when earlier events have left the replay buffer.
• Default new embedded TUI threads to model_reasoning_summary = "detailed", honoring explicit summary settings. Keep concurrent_reasoning_summaries opt-in and disable it when summaries are none.
• Persist the request's captured reasoning summary setting in context updates and local and remote compaction checkpoints.
• Animate status text with a smooth, grapheme-aware shimmer that respects terminal colors and reduced motion.

Testing

Add regression coverage for reasoning status updates, transcript visibility, resume and buffered replay, outbound summary configuration, and summary settings across all three compaction modes. Add shimmer snapshots and checks for smooth brightness changes and Unicode grapheme preservation.