feat: add no-encryption profile option with auto-sourcing support

[youaodu]

Summary

adds support for creating unencrypted profiles and automatic environment variable loading:

• No-encryption profiles: Added --no-encryption / -n flag to create profiles without encryption for development environments
• Auto-sourcing: Environment variables are now automatically applied after envio load without needing to reload shell
• Variable cleanup: Automatically unset old profile variables when switching between profiles

Changes

• Added NoEncryption encryption type that stores profiles in plain text
• Added wrapper function during initialization to auto-source environment variables
• Track loaded variables to clean up when switching profiles
• Updated shell completions (bash, zsh, fish, PowerShell)