feat: complete Phase 12 — voice playback ticker, cache, config, and UI

Add playback position ticker in event loop with 1s UI refresh rate,
integrate VoiceCache for downloaded voice files, add [audio] config
section (cache_size_mb, auto_download_voice), and render progress bar
with waveform visualization in message bubbles.

Fix race conditions in AudioPlayer: add `starting` flag to prevent
false `is_stopped()` during ffplay startup, guard pid cleanup so old
threads don't overwrite newer process pids. Implement `resume_from()`
with ffplay `-ss` for real audio seek on unpause (-1s rewind).

Kill ffplay on app exit via `stop_playback()` in shutdown + Drop impl.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/mod.rs

@@ -107,6 +107,8 @@ pub struct App<T: TdClientTrait = TdClient> {
     pub voice_cache: Option<crate::audio::VoiceCache>,
     /// Состояние текущего воспроизведения
     pub playback_state: Option<crate::tdlib::PlaybackState>,
+    /// Время последнего тика для обновления позиции воспроизведения
+    pub last_playback_tick: Option<std::time::Instant>,
 }
 
 impl<T: TdClientTrait> App<T> {
@@ -126,6 +128,8 @@ impl<T: TdClientTrait> App<T> {
         let mut state = ListState::default();
         state.select(Some(0));
 
+        let audio_cache_size_mb = config.audio.cache_size_mb;
+
         #[cfg(feature = "images")]
         let image_cache = Some(crate::media::cache::ImageCache::new(
             config.images.cache_size_mb,
@@ -169,8 +173,9 @@ impl<T: TdClientTrait> App<T> {
             last_image_render_time: None,
             // Voice playback
             audio_player: crate::audio::AudioPlayer::new().ok(),
-            voice_cache: crate::audio::VoiceCache::new().ok(),
+            voice_cache: crate::audio::VoiceCache::new(audio_cache_size_mb).ok(),
             playback_state: None,
+            last_playback_tick: None,
         }
     }
 
@@ -198,6 +203,7 @@ impl<T: TdClientTrait> App<T> {
             player.stop();
         }
         self.playback_state = None;
+        self.last_playback_tick = None;
         self.status_message = None;
     }