feat: auto focus next pending user action after tool approval/cancellation

[linw1995]

Summary

Automatically focus the next pending user action after tool approval/cancellation, improving workflow efficiency.

Details

• Extract focus_next_pending_user_action_or_input helper for unified focus handling
• Auto-focus next pending action after tool operations; fall back to input if none
• Fix pending action tracking (add/remove tool_use_action)
• Add focus_next_waiting_permission in messages module to search next permission request
• Add 4 test cases for focus behavior verification

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.97080% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.26%. Comparing base (55394f6) to head (daaa767).
⚠️ Report is 3 commits behind head on dev.

Files with missing lines	Patch %	Lines
crates/coco-tui/src/components/chat.rs	90.17%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #179      +/-   ##
==========================================
- Coverage   48.12%   47.26%   -0.87%     
==========================================
  Files         105      108       +3     
  Lines       27916    30196    +2280     
==========================================
+ Hits        13435    14271     +836     
- Misses      14481    15925    +1444     

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