feat: add comprehensive .env.example configuration template

[dev-wei]

Summary

Adds a comprehensive .env.example template file to help users understand and configure all YMemo environment variables without exposing sensitive credentials.

🎯 What's New

• Complete Configuration Template: 35+ environment variables covering all YMemo features
• Security-First Design: No actual credentials, only safe placeholder values
• Comprehensive Documentation: Detailed comments and usage examples for each variable
• Organized Structure: Variables grouped into 10 logical categories

📋 Configuration Categories

Core Settings

• Provider Selection: Choose transcription service (AWS, Azure, Whisper, Google)
• Audio Configuration: Sample rate, channels, format, chunk size

Cloud Providers

• AWS Transcribe: Complete setup including dual-channel and debugging options
• Azure Speech Service: API configuration with speaker diarization
• Future Providers: Whisper and Google Cloud preparations

Advanced Features

• Performance Tuning: Latency, partial results, confidence thresholds
• Database Integration: Supabase configuration for cloud storage
• Development Tools: Testing modes, debugging options, logging levels

🔒 Security Features

• ✅ No Real Credentials: All sensitive values use safe placeholders
• ✅ Security Warnings: Clear reminders about credential safety
• ✅ Best Practices: Guidance on credential management and rotation
• ✅ Usage Examples: Safe configuration scenarios for different setups

📖 User Experience

For New Users

• Copy .env.example to .env and fill in actual values
• Understand all available configuration options
• Get started quickly with example configurations

For Advanced Users

• Access all performance and debugging options
• Configure complex setups like dual-channel AWS processing
• Fine-tune behavior for production environments

For Contributors

• Reference for all supported environment variables
• Documentation of default values and acceptable ranges
• Examples for testing and development setups

🎨 File Structure

# Header with usage instructions
# ======================================================================
# Provider Selection (2 vars)
# Audio Configuration (5 vars) 
# AWS Transcribe (13 vars)
# Azure Speech Service (6 vars)
# Future Providers (3 vars)
# Performance Settings (5 vars)
# Database Configuration (2 vars)
# Logging & Debugging (2 vars)
# Development & Testing (6+ vars)
# Usage Examples
# Security Notes
# Troubleshooting Guide
# ======================================================================

🚀 Benefits

1. Improved Onboarding: New users can understand YMemo configuration at a glance
2. Reduced Support: Self-documenting configuration reduces setup questions
3. Security Improvement: Template prevents accidental credential exposure
4. Feature Discovery: Users learn about advanced features they might not know exist
5. Production Ready: Includes enterprise-grade configuration options

🧪 Test Plan

• File created with comprehensive variable coverage
• All placeholders are safe (no real credentials)
• Documentation is clear and helpful
• Examples cover common use cases
• Security warnings are prominent
• File passes pre-commit hooks

📝 Usage

# Copy the template
cp .env.example .env

# Edit with your actual values
nano .env

# Ensure .env is in .gitignore (it already is\!)

This PR makes YMemo more accessible to new users while maintaining security best practices. The comprehensive documentation should reduce setup friction and help users discover YMemo's full capabilities.

🤖 Generated with Claude Code

[github-actions]

🧪 YMemo CI/CD Results

✅ Tests: success

📊 Test Summary

• Total Tests: 261
• Execution Time: ~8 seconds
• Hardware Dependencies: None (fully mocked)
• Test Categories: Providers, AWS, Audio, Config, Unit

🎯 Quality Standards

YMemo maintains enterprise-grade quality with:

• 99.4% test pass rate requirement
• Comprehensive mocking for CI/CD reliability
• Cross-platform compatibility validation

🎉 All systems go! This PR is ready for review.