Add GET /api/v1/download/linux-package

Redirects to the newest MusicPlayer release's _linux.tar.gz, which has the
icon, a menu entry and install.sh. /download/linux keeps serving the bare
.x86_64, which updating in place needs. Releases without the package get 404.

Closes #34

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/misc_handler.go

@@ -102,4 +102,6 @@ func (s *Server) registerMisc(a huma.API) {
 	}
 	download("download-client-windows", "/download/windows", "Windows", ".exe")
 	download("download-client-linux", "/download/linux", "Linux", ".x86_64")
+	// The package has the icon, a menu entry and install.sh. Releases before 1.9 have none (404).
+	download("download-client-linux-package", "/download/linux-package", "Linux (package with installer)", "_linux.tar.gz")
 }