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.

pockettts.service

@@ -0,0 +1,37 @@
+[Unit]
+Description=Pocket TTS Discord Bot
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+# Replace with your username
+User=YOUR_USERNAME
+Group=YOUR_USERNAME
+
+# Replace with the actual path to your bot directory
+WorkingDirectory=/home/YOUR_USERNAME/PocketTTSBot
+
+# Use the Python from the virtual environment
+ExecStart=/home/YOUR_USERNAME/PocketTTSBot/venv/bin/python bot.py
+
+# Restart on failure
+Restart=on-failure
+RestartSec=10
+
+# Give the bot time to gracefully shutdown
+TimeoutStopSec=30
+
+# Logging
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=pockettts
+
+# Security hardening (optional but recommended)
+NoNewPrivileges=true
+ProtectSystem=strict
+ProtectHome=read-only
+ReadWritePaths=/home/YOUR_USERNAME/PocketTTSBot/voices
+PrivateTmp=true
+
+[Install]
+WantedBy=multi-user.target