- Add case-insensitive matching to partial-word matchers
- Fixes issue where 'search' doesn't match 'Anki-Search-Stats-Extended'
- Uses 'r:|=*' (substring) not 'r:|?=**' (overly permissive) to prevent over-matching
- Maintains 100% backward compatibility with existing completion behavior
- Works in both default and HYPHEN_INSENSITIVE modes
Tested with 35+ test cases covering:
- Original issue scenarios
- Backward compatibility (exact, prefix, suffix, substring matches)
- Edge cases and random scenarios
- Over-matching prevention
- HYPHEN_INSENSITIVE mode
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