Add update notification banner and Check for Updates

[omayaro]

Summary

• On startup, compare the app version to the latest GitHub release and show a dismissible top banner when a newer version exists.
• Help → Check for Updates… opens the GitHub Releases page; banner includes View release and dismiss (×) that remembers the dismissed version.
• About dialog now shows app.getVersion() instead of a hardcoded 1.0.0.

Test plan

• Run an older build (or temporarily lower package version) and confirm the update banner appears
• Dismiss with × and restart — banner stays hidden for that release
• Help → Check for Updates… opens https://github.com/omayaro/all_book_reader/releases
• View release on the banner opens the latest release page
• CI quality gate passes

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