feat/apple music and optimizations

[daimoxd]

Description

This PR introduces a major overhaul of the audio, UI, and backend architecture to achieve extreme memory optimizations (zero-allocation hot paths). Additionally, it integrates a powerful new Apple Music module with a provider selector and a revamped TUI slash-command system.

Apple Music & New TUI Features

• Provider Selector (/provider): Dynamically switch the active catalog between youtube and apple.
• Apple Music Integration (apple.ts, gamdl.ts): Resolves, fetches libraries, and plays Apple Music tracks using gamdl under the hood. Requires authentication cookies to be set via /auth <cookies>.
• Custom applemusic-api: Integrated a custom fork to enable direct fetching from the Apple Music catalog.
• Slash Commands (commands.ts): Added a robust command bar at the bottom (/search, /library, /auth, /pause, /help, etc.).
• Doctor (cli.ts): catunes doctor now checks and reports the status of gamdl.

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Improved Performance & Zero-Allocation Hot Paths

• Audio Engine (audio.ts):
  • Eliminated .map() and new Float64Array() instances on every frame. Pre-allocated _re, _im, _bands, and _wave static buffers.
  • Implemented PcmBuffer: a custom 64KB circular ring-buffer, entirely avoiding costly Buffer.concat() garbage collection cycles during playback.
• Ink / React UI (app.tsx):
  • Adjusted the render tick from 90ms to 120ms (smoother performance, 25% less CPU overhead).
  • Double-buffering: Added index-swapped buffers (specBufRef, peakBufRef) for the React state to stop spreading arrays every tick.
  • Aggressive Memoization: Wrapped Visualizer, PixelCat, NowPlaying, PickList, and Panel in React.memo to drop redundant UI re-renders.
  • Eliminated the spread of player.state object; React now only re-renders when data actually changes.
• Backend Relay (server/index.ts):
  • Implemented cached rosters.
  • Pre-serialized JSON broadcast payloads (_rosterPayload) to avoid recreating objects on every single WebSocket broadcast.
• Caching & I/O (config.ts, playlist.ts, status.ts):
  • In-memory lazy cache for loadSettings() and loadPlaylist(). Writes to disk are now batched to prevent unnecessary I/O.
  • Shared utility fmtTime in fmt.ts to reduce code duplication.

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Documentation

• Updated README.md and README.es.md to properly document the new /auth requirement for Apple Music.
• Rewrote the "Controls" section to highlight the new TUI slash-commands vs CLI mode.
• Updated the Legal Disclaimer to properly address the use of third-party tools like gamdl and local file handling.