perf: memoize PhotoGrid assets map to prevent re-renders during lightbox navigation [#5]

Extracted the grid mapping logic out of the return block into a `useMemo`
hook depending on `[assets, layout, openLightbox]`. This prevents the
entire photo grid—including complex Next.js `<Image>` and `<FadeIn>`
components—from needlessly re-rendering every time the user navigates
via the lightbox arrows or presses next/prev buttons, which previously
caused `lightboxIndex` to update and trigger a re-render of the entire grid.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

.jules/bolt.md

@@ -0,0 +1,4 @@
+## YYYY-MM-DD - [Memoize grid item re-rendering]
+
+**Learning:** `useMemo` can significantly boost the performance of long list or grid components (like `PhotoGrid` component) that otherwise gets re-rendered on simple interactions like navigating the image lightbox. Running standard formatting `pnpm format` applies huge changes across entire directories, so it's generally best to format and clean up ONLY modified files to avoid huge diff pollution in code review.
+**Action:** Be extremely cautious of running format/lint commands at the root codebase; specify only modified directories or files, or avoid formatting if it cascades globally. Focus on targeted memoization where state changes dictate expensive array mapping operations.

app/[...path]/PhotoGrid.tsx

@@ -8,7 +8,7 @@
 
 'use client';
 
-import { useState, useCallback, useEffect } from 'react';
+import { useState, useCallback, useEffect, useMemo } from 'react';
 import Image from 'next/image';
 import { Lightbox } from '@/components/Lightbox';
 import { FadeIn } from '@/components/FadeIn';
@@ -136,10 +136,10 @@ export function PhotoGrid({ assets, layout = 'masonry', gridStyle }: PhotoGridPr
     };
   }, [lightboxIndex, closeLightbox, goNext, goPrev]);
 
-  return (
-    <>
-      <div className={`photo-grid photo-grid--${layout}`} style={gridStyle}>
-        {assets.map((asset, index) => (
+  // Memoize grid items to prevent re-renders of the entire grid (which includes
+  // Image and FadeIn components) when navigating the lightbox.
+  const gridItems = useMemo(() => {
+    return assets.map((asset, index) => (
       <FadeIn key={asset.id} delay={index < 12 ? index * 50 : 0}>
         <div
           className={`photo-grid__item${
@@ -179,7 +179,13 @@ export function PhotoGrid({ assets, layout = 'masonry', gridStyle }: PhotoGridPr
           )}
         </div>
       </FadeIn>
-        ))}
+    ));
+  }, [assets, layout, openLightbox]);
+
+  return (
+    <>
+      <div className={`photo-grid photo-grid--${layout}`} style={gridStyle}>
+        {gridItems}
       </div>
 
       {lightboxIndex !== null && (