feat: add SOCKS proxy support

[scrense-hash]

🔒 SOCKS5 Proxy Support for Session Desktop

Full SOCKS5 proxy implementation with TLS certificate preservation.
All network traffic routes through configured SOCKS proxy with zero traffic leaks.

✨ Features

• ✅ SOCKS5 proxy support with authentication
• ✅ Proper timeout handling for proxy connections (30s vs 5s for direct)
• ✅ TLS/SSL certificate validation through proxy
• ✅ Certificate pinning preservation
• ✅ Agent caching for performance optimization
• ✅ Detailed error logging for debugging
• ✅ UI for proxy configuration in Settings
• ✅ Auto-updater disabled when proxy is enabled (prevents traffic leaks)

🔐 Security

• TLS certificate validation works through SOCKS proxy
• Certificate pinning for seed nodes preserved
• Auto-updater disabled when proxy enabled to prevent bypass
• All traffic (messages, media, metadata) routes through proxy

⚠️ Important

Auto-updates are disabled when proxy is enabled to prevent traffic leaks.
To update Session Desktop while using proxy, download manually from GitHub Releases.

[scrense-hash]

Closing this PR in favor of #1751 which contains the same SOCKS5 proxy implementation but with a cleaner commit history and updated to the latest dev branch.

The new PR includes all the same features:

• SOCKS5 proxy with authentication
• TLS/SSL preservation through proxy
• UI for proxy configuration
• Security improvements (auto-updater disabled when proxy active)

Please review #1751 instead.