feat: Ctrl/Cmd-F focuses vault search; keyboard navigation in results

[pyramation]

Summary

Ctrl/Cmd-F in the Vault screen now focuses (and selects) the search box via a window-level keydown handler, instead of doing nothing.

While focused, the search input gets keyboard completion over the live results (search itself already filters as you type across titles/urls/tags):

• Enter — open the first match
• ArrowDown/ArrowUp — step selection through the result list
• Escape — clear the query and blur

Link to Devin session: https://app.devin.ai/sessions/04636534e07048089ffb6b78142e12cd
Requested by: @pyramation

[devin-ai-integration]

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