Implement chip deletion on backspace for filter labels

[bborn]

Summary

• Implements chip deletion on backspace for project labels in the filter input
• When cursor is positioned right after a ] character, pressing backspace deletes the entire [project] chip plus any trailing space

Implementation Details

• Enhanced the case "backspace": handler in filter mode to detect cursor position relative to chip boundaries
• Searches backward from cursor to find matching [ bracket
• Deletes the entire chip and any trailing space in a single operation
• Maintains existing behavior when cursor is not positioned after a chip

Test Coverage

Added comprehensive test cases covering:

• ✅ Deleting chip at end of input
• ✅ Deleting chip in middle of text
• ✅ Deleting first chip when multiple chips present
• ✅ Deleting second chip when multiple chips present
• ✅ No deletion when cursor not after ]
• ✅ Handling chips without trailing space
• ✅ Handling nested/malformed brackets

Test Results

All existing tests continue to pass, and new test cases verify the chip deletion behavior works correctly.

🤖 Generated with Claude Code