feat: implement Phase 12 — voice message playback with ffplay

Add voice message playback infrastructure:
- AudioPlayer using ffplay subprocess with SIGSTOP/SIGCONT for pause/resume
- VoiceCache with LRU eviction (100 MB limit)
- TDLib integration: VoiceInfo, VoiceDownloadState, PlaybackState types
- download_voice_note() in TdClientTrait
- Keybindings: Space (play/pause), ←/→ (seek ±5s)
- Auto-stop playback on message navigation
- Remove debug_log module

src/tdlib/mod.rs

@@ -19,7 +19,8 @@ pub use client::TdClient;
 pub use r#trait::TdClientTrait;
 pub use types::{
     ChatInfo, FolderInfo, MediaInfo, MessageBuilder, MessageInfo, NetworkState, PhotoDownloadState,
-    PhotoInfo, ProfileInfo, ReplyInfo, UserOnlineStatus,
+    PhotoInfo, PlaybackState, PlaybackStatus, ProfileInfo, ReplyInfo, UserOnlineStatus,
+    VoiceDownloadState, VoiceInfo,
 };
 
 #[cfg(feature = "images")]