fix: Improve keyword filtering to prevent irrelevant chapters

Key improvements to HS code classification:

- Fix irrelevant "Other" chapters appearing (e.g., Ch. 01 for coffee)
  Only add "Other" options from the SAME chapter as matched options

- Implement whole word matching with word boundaries (\b)
  Prevents "tea" matching "teats", "mango" matching "mangolds"

- Add strict plural/suffix matching
  "mango" matches "mangoes" (2 char suffix max) but not "mangolds"

- Add abbreviation matching for long keywords (7+ chars)
  "robusta" can match "Rob" in descriptions

Tested with coffee, tea, mango, robusta - all show relevant options only

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: AryanBV