feat(sanitizer): add iOS Shortcuts `shortcuts:` scheme to validURISchemes

Miniflux sanitizer filters allowed URL schemes, but `shortcuts:` is not included. `shortcuts:` is an official Apple scheme (https://support.apple.com/guide/shortcuts/run-a-shortcut-from-a-url-apd624386f42/ios), similar eg. to already added `itms-apps`

internal/reader/sanitizer/sanitizer.go

@@ -180,6 +180,7 @@ var (
 		"sftp:",
 		"sip:",
 		"sips:",
+		"shortcuts:",
 		"skype:",
 		"spotify:",
 		"ssh:",