unregister coder: URI scheme handler on uninstall of the app

The `coder:` scheme is registered with Windows when you start the Coder Desktop app. We should unregister it when you uninstall the app since we'll be sure you don't need it anymore at that time.

Start by locating the Windows registration for the `coder:` URI scheme and the app's uninstall configuration. Trace how the scheme is registered when Coder Desktop starts, then ensure uninstall removes it; done means the handler is absent after uninstall while normal startup registration still works.

Written by the indexing model from the issue text.