Add self-updating functionality with smtty-update command

[soltros]

Changes:

New Files:

• smtty-update - Standalone updater script that fetches and installs the latest version from GitHub

Modified Files:

• install.sh - Updated to install smtty-update alongside smtty and handle uninstallation

Features:

• One-command updates: Users can run smtty-update to pull the latest version from https://github.com/dillacorn/smtty
• Smart caching: Clones the repository to ~/.cache/smtty-update and reuses it for faster subsequent updates
• Automatic backups: Creates timestamped backups of the current version before updating
• User confirmation: Shows recent commits and asks for confirmation before proceeding
• Self-updating: The updater updates itself along with smtty
• Robust error handling: Handles network failures, corrupted cache, and missing dependencies gracefully
• Colored output: User-friendly colored status messages (INFO, SUCCESS, WARNING, ERROR)
• PREFIX support: Respects the same PREFIX environment variable as install.sh

Usage:

After installing smtty with ./install.sh, users can update at any time by running:

smtty-update

[dillacorn]

We need to also update the uninstall.sh for this to be properly complete.

I reviewed it and I believe everything looks good.. Commiting to main branch