UI: don't capture Alt+left/right (history back/forward) when selecting tabs

Describe the bug

WR view captures Alt+left/right (history back/forward) when handling tabs.

How to reproduce the bug

Browse a WR, e.g. https://debusine.freexian.com/freexian/elts/work-request/16076/
Click on a tab
Left/Right keyboard keys now navigate from one tab to the other
Alt+Left/Right is also captured and prevents me from going back using the reference keyboard shortcut. Which I have to do a lot when browsing debusine results.

Runtime environment

Operating system

Debian Trixie, Firefox.

Versions of debusine and its dependencies

debusine.freexian.com (0.11.4.dev740+g4ffa43dd )

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