Implements #139: full-text search for help topics.
- Add searchIndex with inverted index for fast lookups
- Add tokenize() for case-insensitive word extraction
- Add Search() with relevance ranking:
- Exact word matches score 1.0
- Prefix matches score 0.5
- Title matches get 2.0 boost
- Add snippet extraction for search result context
- Add section-level matching for precise results
- Add comprehensive tests following _Good/_Bad naming
Search features:
- Case-insensitive matching
- Partial word matching (prefix)
- Title boost (matches in title rank higher)
- Section-level results
- Snippet extraction with context
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
