docs: Add Piper TTS status and setup documentation

- Created PIPER_STATUS.md explaining current state and manual setup
- Documented why automatic download doesn't work
- Provided clear step-by-step setup instructions
- Listed alternative (Kokoro TTS) for users who prefer zero-setup
- Added troubleshooting for common errors

Piper TTS is fully functional but requires one-time manual voice model download.

PIPER_STATUS.md

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+# Piper TTS Integration Status
+
+## Current State: ✅ Integrated with Manual Setup Required
+
+Piper TTS has been successfully integrated into the application as an alternative to Kokoro TTS. The integration is **complete and functional**, but requires **manual voice model download** before use.
+
+## What Works
+
+✅ **Backend Integration**
+- PiperTTSService with pitch control (-12 to +12 semitones)
+- UnifiedTTSService managing both engines
+- API endpoints for engine selection
+- Voice preview support for Piper voices
+
+✅ **Frontend Integration**
+- Engine selector UI (Kokoro vs Piper buttons)
+- Dynamic voice loading per engine
+- Visual feedback for active engine
+
+✅ **Documentation**
+- Comprehensive setup guides
+- API documentation
+- Troubleshooting instructions
+
+## What Requires Manual Setup
+
+⚠️ **Voice Models Must Be Downloaded Manually**
+
+Piper voice models cannot be auto-downloaded due to:
+- HuggingFace repository structure complexity
+- SSL certificate verification issues in some environments
+- Large file sizes (10-50MB per voice)
+
+**This is a one-time setup step.**
+
+## How to Use Piper TTS
+
+### Step 1: Install Piper Binary
+
+```bash
+cd backend
+./install_piper.sh
+```
+
+Verify: `piper --version`
+
+### Step 2: Download Voice Models
+
+1. Visit: https://github.com/rhasspy/piper/releases/tag/v1.2.0
+2. Download these files for each voice you want:
+   - `en_US-lessac-medium.onnx` (model file)
+   - `en_US-lessac-medium.onnx.json` (config file)
+
+3. Place in: `backend/piper_models/`
+
+**Recommended starter voices:**
+- `en_US-lessac-medium` (Male, American)
+- `en_US-amy-medium` (Female, American)
+- `en_GB-alan-medium` (Male, British)
+
+### Step 3: Test Installation
+
+```bash
+cd backend
+python test_piper_direct.py
+```
+
+### Step 4: Use in Application
+
+1. Start backend: `uvicorn main:app --reload`
+2. Start frontend: `npm run dev`
+3. In Voice Assignment screen, click "Piper TTS" button
+4. Select Piper voices from dropdown
+5. Generate audiobook with pitch control!
+
+## Why Manual Download?
+
+We attempted automatic download but encountered:
+- **SSL Certificate Issues**: Python's urllib has certificate verification problems
+- **URL Structure**: HuggingFace's repository structure is complex
+- **Reliability**: Manual download is more reliable across different environments
+
+**Trade-off**: One-time manual setup vs. unreliable automatic downloads
+
+## Alternative: Use Kokoro TTS
+
+If Piper setup is too complex, **Kokoro TTS works perfectly out of the box** with:
+- ✅ No manual setup required
+- ✅ 54 voices across 9 languages
+- ✅ High quality synthesis
+- ❌ No pitch control
+
+Simply keep the default "Kokoro TTS" engine selected.
+
+## Error Messages You Might See
+
+### "Voice model not found"
+
+**Cause**: Voice model files not downloaded
+
+**Solution**: Download `.onnx` and `.onnx.json` files and place in `backend/piper_models/`
+
+**See**: `backend/PIPER_SETUP.md` for detailed instructions
+
+### "Piper not found"
+
+**Cause**: Piper binary not installed
+
+**Solution**: Run `./install_piper.sh` or install manually
+
+### "Preview failed"
+
+**Cause**: Voice model missing or Piper not working
+
+**Solution**: 
+1. Check voice models are downloaded
+2. Test with `python test_piper_direct.py`
+3. Check backend logs for detailed errors
+
+## Future Improvements
+
+Potential enhancements for easier setup:
+
+1. **Bundled Voice Models**: Include 1-2 default voices in repository
+2. **Download Script**: Create a helper script to download popular voices
+3. **UI Download**: Add "Download Voice" button in frontend
+4. **Alternative Hosting**: Host models on a simpler CDN
+5. **Docker Image**: Pre-package models in Docker image
+
+## Documentation
+
+- **Setup Guide**: `backend/PIPER_SETUP.md`
+- **Integration Details**: `PIPER_TTS_INTEGRATION.md`
+- **Usage Guide**: `backend/PIPER_TTS_GUIDE.md`
+- **Backend README**: `backend/README.md`
+
+## Support
+
+If you encounter issues:
+
+1. Check `backend/PIPER_SETUP.md` for setup instructions
+2. Run `python test_piper_direct.py` to diagnose problems
+3. Check backend logs for detailed error messages
+4. Fall back to Kokoro TTS if needed
+
+## Summary
+
+**Piper TTS is fully integrated and functional**, but requires a one-time manual setup to download voice models. This is a reasonable trade-off for gaining pitch control capabilities. Users who prefer zero-setup can continue using Kokoro TTS.
+
+**Recommendation**: Document the manual setup clearly in user-facing documentation and consider it a "power user" feature.