New Features:
- Full-text search powered by Tantivy with in-memory indexing
- Chinese word segmentation support via Jieba tokenizer
- Multi-field search across file paths, names, titles, and content
- Search result snippets with keyword highlighting
- Auto-scroll and temporary keyword highlighting on navigation
- Keyboard navigation in search results (↑/↓/Enter)
- Auto-indexing with file watcher for real-time updates
- Clean full-screen search UI with content-width constraint

Improvements:
- Directory mode now supports keyboard shortcuts and search
- Fixed keyboard event listeners initialization in directory pages
- Unified search and keyboard shortcuts styles across all pages

Documentation:
- Added comprehensive search feature documentation
- Updated command line options reference
- Added search usage examples and guides
- Updated tech stack with Tantivy dependencies