Adopt Swift 6 concurrency and harden archive workflows

[lyc280705]

Summary

• adopt Swift 6 strict concurrency with structured, cancellable archive operations
• add secure password handling, cleanup of partial outputs, and stale-progress protection
• improve native menus, accessibility, localization, packaging, and optional Developer ID notarization
• keep macOS 14+, Intel, and Apple Silicon compatibility while using macOS 26 features where appropriate

Verification

• work/CleanZipBuild/tests/run.sh
• work/CleanZipBuild/src/build.sh
• work/CleanZipBuild/src/package.sh
• ZIP/7Z round trips, split archives, encrypted archive retries, cancellation cleanup
• universal x86_64 arm64 binaries and package component validation