fix(updates): restore Sparkle feed for 0.3.2

[lucaslus]

Summary

• point Floatick at the active Sparkle appcast after the GitHub account rename
• add candidate and stable release gates that validate the embedded feed and live XML
• publish 0.3.2+9 metadata and document the one-time manual upgrade for 0.3.0/0.3.1

Verification

• dart format --output=none --set-exit-if-changed lib test integration_test
• flutter analyze
• flutter test (123 tests)
• npm run build (website)
• flutter build macos --release --build-name 0.3.2 --build-number 9
• update feed negative and positive validation
• universal architecture and launch smoke test
• candidate workflow, SHA256, manifest, and packaged Info.plist validation