Update Sparkle to 2.9.4

[SeoFood]

Context

TypeWhisper currently resolves Sparkle 2.8.1. Sparkle 2.9.2 includes two security fixes, and Sparkle 2.9.4 fixes activation of the standard updater UI for backgrounded or dockless applications, which is directly relevant to TypeWhisper as an LSUIElement menu bar app.

This dependency update is intentionally separate from #891. Sparkle 2.9.4 still does not provide an updater(_:feedURLRequest:) delegate hook, so upgrading does not make that implementation valid.

Implementation

• Update the resolved Sparkle package from 2.8.1 to 2.9.4.
• Verify the existing updater integration remains compatible with Sparkle’s Swift concurrency annotations.
• Keep the current stable, release-candidate, and daily update-channel behavior unchanged.

Acceptance criteria

• Package.resolved pins Sparkle 2.9.4 at commit b6496a74a087257ef5e6da1c5b29a447a60f5bd7.
• scripts/pr-preflight.sh passes.
• The development app builds and launches through the standard TypeWhisper dev-build workflow.
• A manual Check for Updates smoke confirms that Sparkle’s standard UI opens correctly from the menu bar app.

References

• https://github.com/sparkle-project/Sparkle/releases/tag/2.9.2
• https://github.com/sparkle-project/Sparkle/releases/tag/2.9.4