fix: save transcript records for failed subagent executions

[linw1995]

Resolves #131

Summary

Fixes missing transcript records when subagent execution fails. The system now properly captures and saves complete transcript information regardless of execution outcome.

Changes

• Ensure transcript events capture subagent execution results even when failures occur
• Save complete execution context including error information for failed tasks
• Improve breadcrumb navigation UI with better padding

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 158 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.46%. Comparing base (a46f02c) to head (89531c0).
⚠️ Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/tools/run_task.rs	0.00%	155 Missing ⚠️
crates/coco-tui/src/components/chat.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #134      +/-   ##
==========================================
- Coverage   50.22%   49.46%   -0.77%     
==========================================
  Files          93       93              
  Lines       25033    25414     +381     
==========================================
- Hits        12574    12572       -2     
- Misses      12459    12842     +383     

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