Fix Piper TTS absolute path resolution and improve deployment workflow

This commit resolves the "download entire voices" issue by properly handling
absolute paths in Piper model configuration and improves the deployment system.

Key changes:
- speech.py: Detect absolute paths and omit --data-dir/--download-dir flags
  when using absolute model paths, allowing Piper to load models directly
- speech.py: Add debug logging and stderr capture for Piper subprocess
- voice_to_speaker.default.yaml: Use absolute paths for all Piper models
- Makefile: Load deployment config from vars.sh for better security
- Makefile: Change restart to rebuild container ensuring code updates apply
- Add vars.sh.example template for deployment configuration
- .gitignore: Add vars.sh to prevent committing deployment secrets

Tested successfully with en_US-libritts_r-medium model using absolute path:
/app/voices/en/en_US/libritts_r/medium/en_US-libritts_r-medium.onnx

🦝 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -1,6 +1,7 @@
 voices/
 .env
 speech.env
+vars.sh
 config/pre_process_map.yaml
 config/voice_to_speaker.yaml