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>

tests/config.rs

@@ -1,6 +1,6 @@
 // Integration tests for config flow
 
-use tele_tui::config::{Config, ColorsConfig, GeneralConfig, ImagesConfig, Keybindings, NotificationsConfig};
+use tele_tui::config::{AudioConfig, Config, ColorsConfig, GeneralConfig, ImagesConfig, Keybindings, NotificationsConfig};
 
 /// Test: Дефолтные значения конфигурации
 #[test]
@@ -35,6 +35,7 @@ fn test_config_custom_values() {
         keybindings: Keybindings::default(),
         notifications: NotificationsConfig::default(),
         images: ImagesConfig::default(),
+        audio: AudioConfig::default(),
     };
 
     assert_eq!(config.general.timezone, "+05:00");
@@ -120,6 +121,7 @@ fn test_config_toml_serialization() {
         keybindings: Keybindings::default(),
         notifications: NotificationsConfig::default(),
         images: ImagesConfig::default(),
+        audio: AudioConfig::default(),
     };
 
     // Сериализуем в TOML