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/ui/messages.rs

@@ -234,6 +234,7 @@ fn render_message_list<T: TdClientTrait>(f: &mut Frame, area: Rect, app: &mut Ap
                     app.config(),
                     content_width,
                     selected_msg_id,
+                    app.playback_state.as_ref(),
                 );
 
                 // Собираем deferred image renders для всех загруженных фото