- Add in-memory LRU cache (200 entries, 30 min TTL) to yt-dlp Client for
GetMediaInfo and GetPlaylistInfo results, avoiding redundant yt-dlp calls
for the same URL within a session
- Add YouTube (/search) and YouTube Music (/music) search with paginated
results (5 per page), user selects a result to start the download flow
- Add SearchState type, new search.go handler, search results keyboard with
< > navigation and New Search button
- Add Search button to main menu keyboard
- Update help text with new commands
