art: desktop zoom in the lightbox (pan-by-cursor), mobile keeps pinch

The full-screen lightbox showed the framed piece capped at ~66vh, so on desktop it was
barely larger than the page view and there was no way to inspect detail (mobile can pinch).
Add a "Zoom in" affordance: it swaps to a magnified inspection view (full-res image scaled
2.5×) where moving the cursor pans via transform-origin; click or Escape steps back to the
framed view, Escape/✕/backdrop close. Restructured the lightbox from a single <button> to a
dialog (backdrop button + close button + stage) so the controls are valid/accessible. Zoom
button hidden on touch (hover:none) — native pinch covers mobile. Uses the already-cached
full-res copy (/api/art/image/<id>?size=full); fade-in, frame/thickness, rotate-on-portrait
all preserved.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/art/+page.svelte

@@ -27,9 +27,25 @@
   // screens; desktop and portrait art stay upright). Aspect is read off the loaded image.
   let landscape = $state(false);
 
-  function onKey(e) {
+  // Desktop zoom: inside the lightbox, magnify the artwork and pan by moving the cursor
-    if (e.key === 'Escape' && zoom) zoom = false;
+  // (transform-origin tracks the pointer). Mobile keeps native pinch — the Zoom button is
+  // hidden there. ox/oy are the transform-origin in %.
+  let zoomed = $state(false);
+  let ox = $state(50), oy = $state(50);
+  function enterZoom() { ox = 50; oy = 50; zoomed = true; }
+  function panZoom(e) {
+    const r = e.currentTarget.getBoundingClientRect();
+    ox = Math.max(0, Math.min(100, ((e.clientX - r.left) / r.width) * 100));
+    oy = Math.max(0, Math.min(100, ((e.clientY - r.top) / r.height) * 100));
   }
+
+  function onKey(e) {
+    if (e.key !== 'Escape') return;
+    if (zoomed) zoomed = false;        // Escape steps out of zoom first, then closes
+    else if (zoom) zoom = false;
+  }
+  // Leaving the lightbox always drops zoom too, so re-opening starts framed.
+  $effect(() => { if (!zoom) zoomed = false; });
   // Move focus to the lightbox when it opens, so Escape/Enter work and focus is trapped sanely.
   $effect(() => { if (zoom && lightboxEl) lightboxEl.focus(); });
 
@@ -218,15 +234,33 @@
 </div>
 
 {#if zoom && art}
-  <button class="lightbox" class:rotate={landscape} bind:this={lightboxEl} onclick={() => (zoom = false)} aria-label="Close artwork">
+  <div class="lightbox" class:rotate={landscape && !zoomed} class:zoomed bind:this={lightboxEl}
-    <span class="lb-stage">
+       tabindex="-1" role="dialog" aria-modal="true" aria-label="{art.title}, full screen">
-      <span class="frame frame--{frame} lb-frame" style="--frame-scale:{thickness}">
+    <button class="lb-backdrop" onclick={() => (zoom = false)} aria-label="Close artwork"></button>
-        {#if isWood}{@render woodRails()}{/if}
+    <button class="lb-close" onclick={() => (zoom = false)} aria-label="Close">
-        <span class="mat"><img src={art.image_url_large || art.image_url} alt={art.title} /></span>
+      <svg viewBox="0 0 24 24" width="18" height="18" fill="none" stroke="currentColor" stroke-width="2.2" stroke-linecap="round" aria-hidden="true"><path d="M6 6l12 12M18 6L6 18" /></svg>
+    </button>
+    {#if zoomed}
+      <!-- magnified inspection view: move the cursor to pan, click to zoom back out -->
+      <button class="lb-zoom" onpointermove={panZoom} onclick={() => (zoomed = false)} aria-label="Zoom out">
+        <img src={art.image_url_large || art.image_url} alt={art.title}
+             style="transform-origin:{ox}% {oy}%" draggable="false" />
+      </button>
+      <span class="lb-hint">Move to look closer · click to zoom out</span>
+    {:else}
+      <span class="lb-stage">
+        <span class="frame frame--{frame} lb-frame" style="--frame-scale:{thickness}">
+          {#if isWood}{@render woodRails()}{/if}
+          <span class="mat"><img src={art.image_url_large || art.image_url} alt={art.title} /></span>
+        </span>
+        <span class="lb-cap">{art.title}{#if art.artist}<span class="sep">·</span>{art.artist}{/if}</span>
+        <button class="lb-zoombtn" onclick={enterZoom}>
+          <svg viewBox="0 0 24 24" width="15" height="15" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><circle cx="11" cy="11" r="7" /><path d="M21 21l-3.5-3.5M11 8v6M8 11h6" /></svg>
+          Zoom in
+        </button>
       </span>
-      <span class="lb-cap">{art.title}{#if art.artist}<span class="sep">·</span>{art.artist}{/if}</span>
+    {/if}
-    </span>
+  </div>
-  </button>
 {/if}
 
 <style>
@@ -491,20 +525,48 @@
   .note { color: var(--muted); font-size: 1.05rem; margin-top: 40px; }
 
   .lightbox {
-    position: fixed; inset: 0; z-index: 50; border: none; cursor: zoom-out;
+    position: fixed; inset: 0; z-index: 50;
     /* A soft, top-lit gallery wall — lighter than the page so every frame (Black
        included) reads, like a piece hung on a real wall. */
     background: linear-gradient(180deg, #efe9dd, #e2dbcc);
     display: flex; flex-direction: column;
     align-items: center; justify-content: center; padding: 2.5vmin;
   }
+  /* full-bleed click target behind the content — clicking the wall closes */
+  .lb-backdrop { position: absolute; inset: 0; z-index: 0; border: none; background: none; padding: 0; cursor: zoom-out; }
+  .lb-close {
+    position: absolute; top: clamp(10px, 2vw, 20px); right: clamp(10px, 2vw, 20px); z-index: 3;
+    width: 40px; height: 40px; border-radius: 999px; border: 1px solid rgba(40, 30, 20, 0.12);
+    background: rgba(255, 255, 255, 0.72); color: #3a3a3a; cursor: pointer;
+    display: flex; align-items: center; justify-content: center;
+  }
+  .lb-close:hover { background: #fff; }
   /* frame + caption travel together so a rotated view turns as one piece */
-  .lb-stage { display: flex; flex-direction: column; align-items: center; gap: 12px; }
+  .lb-stage { position: relative; z-index: 1; display: flex; flex-direction: column; align-items: center; gap: 12px; }
+  /* magnified inspection view (desktop): cursor pans via transform-origin */
+  .lb-zoom {
+    position: relative; z-index: 1; width: 96vw; height: 88vh; overflow: hidden;
+    border: none; background: none; padding: 0; cursor: zoom-out;
+    display: flex; align-items: center; justify-content: center;
+  }
+  .lb-zoom img {
+    max-width: 100%; max-height: 100%; width: auto; height: auto; object-fit: contain;
+    transform: scale(2.5); will-change: transform; user-select: none; -webkit-user-drag: none;
+  }
+  .lb-hint { position: relative; z-index: 1; margin-top: 10px; color: #5b636e; font-size: 0.85rem; }
+  .lb-zoombtn {
+    display: inline-flex; align-items: center; gap: 7px; cursor: pointer;
+    border: 1px solid #d9cdeb; background: #fff; color: var(--accent);
+    border-radius: 999px; padding: 8px 16px; font-family: inherit; font-size: 0.9rem; font-weight: 600;
+    transition: background 0.14s ease, color 0.14s ease;
+  }
+  .lb-zoombtn:hover { background: var(--accent); color: #fff; border-color: var(--accent); }
+  @media (hover: none) { .lb-zoombtn { display: none; } }   /* mobile keeps native pinch-zoom */
   /* The full-screen view wears the same frame. Rail + mat are only a touch larger than the
      page (keeping the ~1:1 wood:white proportion), and the image is capped so the whole
      framed piece — including the bottom rail — always fits on screen. */
   .lb-frame {
-    cursor: zoom-out; max-width: 92vw;
+    max-width: 92vw;
     --rail: calc(clamp(18px, 1.9vw, 36px) * var(--frame-scale, 1));
     --mat: calc(clamp(16px, 1.6vw, 30px) * min(var(--frame-scale, 1), 1.5));
   }