fix(nav): Restore focus to previous element after closing command palette

[jshchnz]

Summary

• When the new command palette closes, focus now returns to the element that was focused before it opened
• The GlobalModal's focus-trap doesn't reliably handle this because the palette input's autoFocus moves focus into the portal before the trap's activate() runs, causing it to store the wrong "previous" element
• Saves document.activeElement explicitly when opening the palette and restores it when the modal closes (via any method: Escape, backdrop click, Cmd+K toggle, route change)

Depends on #111441

Test plan

• Focus on search query builder → Cmd+K → close palette → focus returns to search input
• Focus on a button → Cmd+K → Escape → focus returns to button
• Focus on an input → Cmd+K → click backdrop → focus returns to input
• Open palette with no specific focus → close → no error thrown

[JonasBa]

Requesting changes because this landed in #111542 and fixed the behavior for all modals

[getsantry]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀