Integrate Sparkle auto-updates for macOS Developer ID builds

New Release-DeveloperID configuration gates Sparkle behind a SPARKLE
compile flag so the App Store Release build stays Sparkle-free. Adds
SPUStandardUpdaterController wrapper, Check for Updates menu command,
Advanced Settings section with beta channel toggle, and a Ruby script
plus GitHub Actions job that signs each release and publishes the
appcast to gh-pages for consumption by Sparkle and Homebrew cask.

Yattee/YatteeApp.swift

@@ -310,6 +310,11 @@ struct YatteeApp: App {
             CommandGroup(replacing: .appSettings) {
                 SettingsWindowMenuItem()
             }
+            #if SPARKLE
+            CommandGroup(after: .appInfo) {
+                CheckForUpdatesMenuItem()
+            }
+            #endif
         }
         #endif
     }