feat: Integrate Velopack installer and auto-updater

[spektor56]

Integrates Velopack into the OpenpilotToolkit application to provide a streamlined installer and automatic updates on startup.

Key changes:

• Adds Velopack dependency to OpenpilotToolkit.csproj.
• Configures VelopackApp.Build().Run() at app startup in Program.cs.
• Implements background updater logic inside OpenpilotToolkitForm_Load using UpdateManager referencing the spektor56/openpilottoolkit GitHub repository.
• Non-blocking UI prompts user about updates, then downloads and automatically restarts the application.
• Updates the manual-release.yml GitHub action to use vpk pack for creating an installer branded with the repo's icon and splash screen.

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PR created automatically by Jules for task 16694253700221158326 started by @spektor56

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