Fix: Desktop app menus only work on macOS, windows have rendering issues

[JRH89]

Problem Description

The OpenCode desktop app has critical issues on non-macOS platforms:

Current Issues

• Menus only work on macOS: Windows and Linux users get no menus at all
• Window rendering problems: Title bar and window decorations have rendering issues
• Poor error handling: Menu actions fail silently without user feedback
• Window creation conflicts: App fails to start due to duplicate window creation

Expected Behavior

• Menus should work on all platforms (Windows/Linux/macOS)
• Windows should render properly with correct title bars
• Users should get feedback when actions fail
• App should start reliably across all platforms

Platform Details

• Linux: No menus, window rendering issues
• Windows: Likely affected (based on code analysis)
• macOS: Works but could benefit from better error handling

Root Cause Analysis

The code has macOS-specific restrictions:

Plus window configuration conflicts between Tauri config and Rust code.

Impact

This makes the desktop app essentially unusable for Windows/Linux users, which is a significant portion of the potential user base.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Windows Support #631: Windows Support (super issue tracking all Windows-related problems)
• White screen on launch – OpenCode Desktop (Windows 10) #9577: White screen on launch – OpenCode Desktop (Windows 10) (same rendering/window issue on Windows)
• Blank screen on opencode desktop on Linux(Ubuntu) #5683: Blank screen on opencode desktop on Linux(Ubuntu) (similar blank/rendering issue on Linux)

Feel free to ignore if none of these address your specific case.