Add cross-platform support for Linux

[chadthomas31]

🐧 Add Linux Cross-Platform Support

📋 Addresses Q1 2026 Roadmap Item: This PR implements Linux support as outlined in the project roadmap.

🎯 Problem

Currently, mailstorm only runs on Windows due to:

• Windows-specific imports (winreg)
• Hard-coded Windows Tor paths
• WebView2 dependencies
• Windows-specific subprocess handling

✅ Solution

Made the application platform-aware with conditional logic for Windows vs Linux.

Changes:

• Make winreg import conditional (Windows only)
• Add platform-specific Tor paths (tor/tor for Linux, .exe for Windows)
• Skip WebView2 check/install on non-Windows systems (uses GTK webkit instead)
• Remove Windows-specific STARTUPINFO on Linux
• Add Linux-compatible proxy settings for GTK webkit
• Create build.sh for Linux builds with PyInstaller
• Add .gitignore for build artifacts and Tor bundles

🧪 Testing

• ✅ Tested on Pop_OS 22.04 (Ubuntu-based)
• ✅ Successfully launches Tor and bootstraps to 100%
• ✅ Connects to .onion site through Tor proxy
• ✅ GTK webview renders correctly
• ✅ Built with PyInstaller 6.17.0
• ✅ Used Tor Expert Bundle 15.0.3 for Linux (x86_64)

📋 Linux Setup Instructions

Dependencies:

sudo apt install python3-gi python3-gi-cairo gir1.2-gtk-3.0 gir1.2-webkit2-4.0
pip install -r requirements.txt

Build:

# Download Tor Expert Bundle for Linux from torproject.org
# Extract to mailstorm/tor/
chmod +x build.sh
./build.sh
./dist/main

🤝 Backwards Compatibility

All Windows functionality remains unchanged. The app detects the platform at runtime and uses appropriate code paths.

📸 Screenshot

Application running successfully on Linux:

• Tor bootstrapped to 100%
• GTK webview displaying .onion site
• Email validation working through Tor proxy