Fix browser compatibility and update button persistence

- Replaced AbortSignal.timeout() with AbortController for broader browser support
- Fixed promise chaining for proper cleanup of timeout handlers
- Added localStorage persistence for update information
- Made update button display more reliable with forced display styles
- Added ID to version elements for easier targeting
- Improved version number synchronization across UI elements

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

public/index.html

@@ -658,7 +658,7 @@
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                 <div class="text-center mt-4">
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+                    <p><strong id="about-version">Transmission RSS Manager v2.0.10</strong></p>
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