## 1. Environment Setup
- [x] 1.1 Create `environment.yml` with Python 3.10, PyQt6, edge-tts, pandas, openpyxl
- [x] 1.2 Test conda environment creation and activation

## 2. Excel Input Module
- [x] 2.1 Implement Excel file loading with openpyxl/pandas
- [x] 2.2 Implement column parsing (Filename, Text, Lang)
- [x] 2.3 Add data validation for required fields
- [x] 2.4 Implement default language fallback (zh)

## 3. TTS Engine Module
- [x] 3.1 Define voice registry with all available voices and bilingual support annotations
- [x] 3.2 Implement default voice mapping dictionary (zh/vi/en -> Voice ID)
- [x] 3.3 Implement edge-tts wrapper for voice synthesis with configurable voice
- [x] 3.4 Add rate limit delay (0.5s between requests)
- [x] 3.5 Implement network error handling with retry
- [x] 3.6 Add output directory creation logic

## 4. Threading Model
- [x] 4.1 Create TTS Worker class extending QThread
- [x] 4.2 Implement asyncio event loop within worker thread
- [x] 4.3 Define pyqtSignal for progress, log, completion events
- [x] 4.4 Implement stop flag for graceful cancellation

## 5. GUI Implementation
- [x] 5.1 Create main window with PyQt6
- [x] 5.2 Add file browser widget with .xlsx filter
- [x] 5.3 Add voice selection dropdown (grouped by language, with bilingual annotations)
- [x] 5.4 Add Start/Stop buttons with state management
- [x] 5.5 Add progress bar widget
- [x] 5.6 Add log console (QTextEdit) with auto-scroll
- [x] 5.7 Connect signals to UI update slots
- [x] 5.8 Implement completion notification dialog

## 6. Integration
- [x] 6.1 Wire Excel parser to TTS worker
- [x] 6.2 Pass selected voice from GUI to TTS worker
- [x] 6.3 Connect worker signals to GUI updates
- [x] 6.4 Implement start/stop button handlers

## 7. Testing & Documentation
- [x] 7.1 Create `template.xlsx` with sample data
- [x] 7.2 Test batch processing with 10+ items
- [x] 7.3 Test voice selection (verify different voices produce correct output)
- [x] 7.4 Test UI responsiveness during processing
- [x] 7.5 Test stop functionality mid-batch
- [x] 7.6 Test error handling (invalid file, network error)
- [x] 7.7 Write README.md with usage instructions (including voice selection guide)