fix(web): keep highlights card active index in range on refresh

[abhay-codes07]

Problem

HighlightsCard tracks the visible highlight with activeIndex, and derives currentItem = items[activeIndex]. When items changes, the effect keyed on [items] resets the reply and expansion state but never touches activeIndex:

useEffect(() => {
  setIsReplyOpen(false)
  setReplyText("")
  setIsExpanded(false)
}, [items])

The Daily Brief "refreshes automatically every few hours" (per the card's own info popover), which replaces items wholesale. If the user has paged to a later highlight and the refresh returns a shorter list, activeIndex is left pointing past the end. currentItem becomes undefined, and the render falls through to:

if (!currentItem || items.length === 0) {
  return ( /* "Add some documents to see highlights here" empty state */ )
}

So the card shows the empty "add documents" state even though highlights exist. The pagination row is only rendered in the populated branch, so there is no visible control to page back into range — the card stays stuck on the empty state until it remounts.

Repro

1. Have at least 2 highlights so the pager shows.
2. Page to the last highlight (activeIndex > 0).
3. Let the brief refresh (or simulate it) with fewer highlights than the current activeIndex + 1.

Result on main: the card renders "Add some documents to see highlights here" despite having highlights, with no way to recover in-place. The same happens for any parent that swaps items for a shorter array while the user is on a later page.

Fix

Clamp activeIndex into range whenever items changes, next to the existing reset:

setActiveIndex((i) => Math.min(i, Math.max(items.length - 1, 0)))

This keeps the current position when it is still valid and only pulls it back when the list shrank. When items is genuinely empty it resolves to 0, and the existing items.length === 0 guard renders the empty state correctly.

Also removes a useExhaustiveDependencies suppression that is no longer needed: the effect body now reads items.length, so items is a real dependency rather than a suppressed one.

No test is included because apps/web has no component test harness set up; the change is a two-line clamp mirroring the same pattern used elsewhere for selection bounds. cc @MaheshtheDev @ishaanxgupta

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