fix: Don't prevent non-handled keys

[rijkvanzanten]

We were using .prevent which stops all keydown events, including tabbing when going through a page. This ensures we only call preventDefault when a key was pressed we're handling.

Fixes #31

[Copilot]

Pull Request Overview

This PR fixes an accessibility issue where the split panel component was preventing all keydown events, including navigation keys like Tab. The fix ensures only handled keys (arrow keys, Home, End, Enter) have their default behavior prevented while allowing other keys to function normally.

• Moved preventDefault call inside the key handling logic to only apply to handled keys
• Removed the .prevent modifier from the template to allow unhandled keys to bubble up

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