added mica alt#17650

[ayush45-ui]

I created a complete implementation of Windows 11 Mica Alt backdrop material support for native Windows applications. This enables modern, fluent design integration using the Desktop Window Manager (DWM) API.
Changes Made

1. Core Implementation

Added DWM attribute constants for backdrop control (DWMWA_SYSTEMBACKDROP_TYPE = 38)
Created backdrop type enumeration with 5 options: Auto, None, Mica, Mica Alt, and Tabbed
Implemented functions to apply Mica Alt, standard Mica, and remove backdrops
Added Windows 11 version detection (Build 22000+)
Built fallback mechanism for older Windows 11 builds using legacy DWMWA_MICA_EFFECT

2. Language Support
   Provided implementations in three formats:

C# (WPF): Full class with P/Invoke declarations and UI integration
C++ (Win32): Header-only implementation with WinMain example
JSON: Configuration documentation and API specifications

3. Key Features

Multi-backdrop support (switch between Mica, Mica Alt, Tabbed at runtime)
Automatic OS compatibility checking
Error handling and validation
Easy one-line integration: ApplyMicaAlt(window)

Material Differences
Mica (Standard):

Lighter, more transparent appearance
Subtle desktop wallpaper tinting
Best for main application windows

Mica Alt:

Darker, more opaque variant
Reduced wallpaper influence
Ideal for secondary windows, dialogs, sidebars

References
Official Microsoft Documentation

DwmSetWindowAttribute function

https://learn.microsoft.com/en-us/windows/win32/api/dwmapi/nf-dwmapi-dwmsetwindowattribute
Core API for setting window attributes

Apply Mica or Acrylic materials in desktop apps

https://learn.microsoft.com/en-us/windows/apps/design/style/mica
Official guide for implementing Mica materials

DWM_SYSTEMBACKDROP_TYPE enumeration

https://learn.microsoft.com/en-us/windows/win32/api/dwmapi/ne-dwmapi-dwm_systembackdrop_type
Backdrop type values documentation

Windows 11 Design Principles

https://learn.microsoft.com/en-us/windows/apps/design/signature-experiences/design-principles
Fluent Design System overview

Community Resources

Windows App SDK Samples

https://github.com/microsoft/WindowsAppSDK-Samples
Official Microsoft code samples

Technical Requirements

Minimum OS: Windows 11 Build 22000
Full Mica Alt Support: Build 22621 (22H2 update)
DWM Composition: Must be enabled
Window Type: Non-layered windows only

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