dim-unfocused-windows@retiarylime: Add new extension, initial release

[retiarylime]

Pull Request: Add Dim Unfocused Windows Extension

🎯 Extension Overview

This PR adds a new Cinnamon extension called "Dim Unfocused Windows" that automatically dims unfocused windows to enhance visual clarity and reduce distractions, making it easier to identify the active window.

📋 What This Extension Does

• Automatic Dimming: Windows automatically become semi-transparent and darker when they lose focus
• Dual Visual Effects: Combines both opacity reduction (transparency) and brightness reduction (darkening) for enhanced visual separation
• Smooth Animations: Configurable transition animations with multiple easing options, now with improved brightness animation system
• Smart Filtering: Automatically excludes dialog windows, minimized windows, and windows with specific titles using comma-separated pattern matching (e.g., "Picture in picture,Calculator")
• Enhanced Window Filtering: Better default exclusions including "Picture in picture" windows and more robust filtering logic
• Keyboard Toggle: Quick shortcut (Super+Shift+D) to temporarily enable/disable dimming
• Real-time Settings: All changes apply immediately without requiring a restart, with more descriptive tooltips and settings descriptions

📸 Screenshots