feat: local TTS via piper subprocess with Google fallback

- New src/tts.rs: centralize TTS in synthesize(config, http_client, text)
  Piper subprocess primary, Google Translate fallback on error/missing
- TTS_MODEL_PATH/TTS_VOICE env config (defaults to pl_PL-bass-high)
- Fix Unknown interaction errors: spawn play_tts_in_channel in background
  so voice-state TTS no longer blocks the shard event loop (3s Discord limit)
- Best-effort confirmation replies in /tts to prevent error cascade
- Custom on_error handler: graceful interaction-expired error handling
- Comprehensive tracing logging (engine, model, duration, stderr)

1 files changed, 1 insertions, 1 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 8bc2ab8..10dbabe 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4391,7 +4391,7 @@ dependencies = [
 
 [[package]]
 name = "senator-sperma"
-version = "0.2.5"
+version = "0.3.0"
 dependencies = [
  "chrono",
  "cron",