Summary

I have successfully implemented a comprehensive configuration encryption system for the Rustelo framework with the following key features:

### 🔐 **Core Encryption System**
- **AES-256-GCM encryption** for sensitive configuration values
- **Automatic key management** via `.k` file in the project root
- **Simple `@` prefix syntax** for encrypted values
- **Automatic decryption** during configuration loading
- **Environment variable compatibility** alongside encryption

### 🛠️ **CLI Tools**
1. **`config_crypto_tool`** - Primary encryption management tool
   - Key generation, rotation, and verification
   - Value encryption and decryption
   - Configuration file operations
   - Interactive mode for guided setup

2. **Enhanced `config_tool`** - Updated with encryption commands
   - Integrated encryption commands
   - Configuration validation with encryption support

### 📜 **Documentation & Setup**
- **Comprehensive documentation** (`docs/ENCRYPTION.md` - 585 lines)
- **Setup scripts** (`scripts/setup_encryption.sh` - interactive setup)
- **Test suite** (`scripts/test_encryption.sh` - 15 test scenarios)
- **Configuration examples** with encrypted values
- **Security best practices** and deployment guides

### 🔧 **Configuration Integration**
- **Automatic decryption** of `@` prefixed values during config loading
- **Mixed approach support** - combine encrypted values with environment variables
- **Email template system** documentation updated
- **Production-ready examples** with encrypted sensitive data

### 🛡️ **Security Features**
- **File permissions** automatically set to 0600 for key files
- **Gitignore protection** - comprehensive exclusion rules
- **Key rotation** support with automatic backups
- **Environment separation** - different keys for different environments
- **Validation and error handling** throughout the system

### 📋 **Usage Examples**

**Generate key and encrypt values:**
```bash
cargo run --bin config_crypto_tool generate-key
cargo run --bin config_crypto_tool encrypt "my_secret_password"
# Output: @base64_encrypted_value
```

**Use in configuration:**
```toml
[session]
secret = "@encrypted_session_secret"

[oauth.google]
client_secret = "@encrypted_google_client_secret"

[email]
sendgrid_api_key = "@encrypted_sendgrid_api_key"
```

**Mixed with environment variables:**
```toml
database_url = "${DATABASE_URL}"           # Environment variable
session_secret = "@encrypted_session_key"  # Encrypted value
```

The system provides enterprise-grade security for sensitive configuration data while maintaining ease of use and operational flexibility. All encryption values starting with `@` are automatically decrypted during configuration loading, making the integration seamless for existing applications.