Add 29 tests covering TextArea functionality:
- Basic operations: creation, text manipulation, char insertion
- Cursor movement (left/right/up/down, home/end, word navigation)
- Selection and clipboard (copy/cut/paste)
- Undo/redo operations
- Line deletion (word backward, to line start/end)
- Configuration (placeholder, tab width, viewport)
- Unicode support and multiline editing
Fix overflow bug in delete_to_line_start where undo position
was calculated after text modification.
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Co-Authored-By: Claude <noreply@anthropic.com>
f1dd7d4164