fix(web): reset command palette selection when the result list changes

[abhay-codes07]

What

The documents command palette keeps a selectedIndex into its item list, and the effect commented "Reset selection on items change" has an empty dependency array — so it only ever runs on mount:

// Reset selection on items change
useEffect(() => {
    setSelectedIndex(0)
}, [])

Arrow down to row 5 of the recent-documents list, then type a query that returns two results: selectedIndex stays 5, the highlight disappears (no row renders data-index="5"), and Enter silently does nothing because items[5] is undefined. The selection also never snaps back to the top result when fresh results stream in.

Fix

Two small effects that match the comment's intent:

• snap the selection to the top whenever the query text changes
• clamp it into range whenever the item list shrinks (async search results replacing the recent docs, refetches while the palette is open)

Clamping rather than always resetting keeps the cursor position stable when the list merely refreshes without shrinking.

Testing

• bun test in apps/web — 37 pass
• bun run build in apps/web — clean
• biome check on the touched file — clean (the one remaining warning about items in handleKeyDown deps predates this change)

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