feat: Implement multi-voice support and management

Refactor the TTS handling to support multiple, user-selectable voices. This replaces the previous single-voice system.

Key changes:
- Introduce VoiceManager to handle loading and managing voices from a dedicated oices/ directory.
- Add slash commands (/voice list, /set, /current, /refresh) for users to manage their personal TTS voice.
- Implement on-demand voice loading to improve startup time and memory usage.
- Remove the old 	ts_handler.py and single voice .wav files in favor of the new system.
- Update configuration to specify a voices directory instead of a single file path.

voices/preferences.json

@@ -0,0 +1,5 @@
+{
+  "user_voices": {
+    "122139828182712322": "hankhill"
+  }
+}