Migrate container app to native SwiftUI implementation

Replaced WebView-based app container with a native SwiftUI implementation, significantly reducing code complexity and improving performance.

- Reduced app code from ~290 lines to 91 lines
- Leverages platform-native UI framework for better integration
- Simplifies overall application architecture

Author: bartTC

CHANGELOG.md

@@ -14,6 +14,7 @@ All notable changes to this project will be documented in this file.
 - Headers now displayed in Title-Case (e.g., Cache-Control instead of cache-control)
 - New app icon
 - Simplified and cleaned up popup.js code
+- Replaced WebView-based container app with native SwiftUI (~290 lines → 91 lines)
 
 ### Fixed
 - Toolbar icon appearing blue instead of gray (Safari grayscale tinting workaround)