Avoid extra expanded image dialog rerenders

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What Changed

• Removed the derived-state useEffect from ExpandedImageDialog so new preview props render directly instead of committing once with stale local state and again after the effect.
• Kept local left/right image navigation state scoped to the currently displayed preview.
• Moved the global keyboard listener into a named hook and used useEffectEvent so the subscription stays stable while reading the latest close/navigation behavior.

Why

React Doctor flagged ExpandedImageDialog for derived state in an effect. That pattern caused an avoidable extra render/commit whenever the parent selected a different image preview. The new render-time derivation preserves local navigation while removing the sync effect and its extra commit.

React Doctor follow-up:

• Before: src/components/chat/ExpandedImageDialog.tsx had no-derived-state-effect.
• After: no ExpandedImageDialog diagnostics; package scan went from 753 warnings / 255 files to 752 warnings / 254 files.

UI Changes

React Scan recordings are included in this PR:

• Before: docs/react-scan-recordings/expanded-image-before.webm
• After: docs/react-scan-recordings/expanded-image-after.webm

Both recordings use the same React Scan-enabled harness. Over the same 7s preview-rotation interval, the ExpandedImageDialog subtree committed 13 times before and 7 times after.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Verification:

• bun fmt
• bun lint
• bun typecheck

  

Note

Reduce rerenders in ExpandedImageDialog by extracting navigation and keyboard shortcut hooks

• Extracts image navigation state into a new useExpandedImagePreviewNavigation hook that tracks a (sourcePreview, index) tuple, realigning to the incoming prop's index only when the source preview reference changes.
• Extracts keyboard handling into a new useExpandedImageKeyboardShortcuts hook that attaches a single keydown listener for the dialog's lifetime, using useEffectEvent so callbacks always capture the latest state without re-registering.
• Removes local preview state and its synchronization effect from ExpandedImageDialog, eliminating the rerender cycle they caused.

^{Macroscope summarized 43501dc.}