fix(images): release a collection viewer image Viewer.js has not built yet

Leaving a viewer image while it was still loading (Previous, Next, the
arrow keys, Retry) deferred the inline Viewer.js destroy() until the
image's view settled, failed or a 10 s fallback ran. Before its image
loads Viewer.js has not built, so nothing could settle: the stage
dropped the image, the late load ran Viewer.js's build() on an image
without a parent, and getComputedStyle(null) threw a page error
("Argument 1 is not an object" in Firefox, "must be an instance of
Element" in WebKit). Under CI load this failed "collection viewer
follows filtered loaded order beyond mounted cards".

A viewer that is not ready yet is now destroyed at once, which cancels
its pending build, and its image src is released. A built viewer with
a still-loading view keeps the existing deferral.

web/js/workspace/media-viewer.mjs

@@ -176,10 +176,12 @@ export function createMediaViewer({api,container,parentScope,inspectionControlle
                 const observer = new ResizeObserver(scheduleFit);observer.observe(stage);
                 viewer = instance;mediaLocal.cleanup(() => {
                     observer.disconnect();cancelAnimationFrame(fitFrame);
-                    // Inline Viewer.js keeps viewing a still-loading image after destroy(), and that view
-                    // rebuilds its list from images that still have a src; keep both until the view
-                    // settles, fails or times out.
-                    if (viewSettled) { release(); return; }
+                    // Before Viewer.js has built (its image still loading), destroy() cancels the pending build;
+                    // deferring it would let the late load build into the image the stage has just dropped.
+                    // Once built, inline Viewer.js keeps viewing a still-loading image after destroy(), and that
+                    // view rebuilds its list from images that still have a src; keep both until the view settles,
+                    // fails or times out.
+                    if (viewSettled || !instance.ready) { release(); return; }
                     node.addEventListener('error',release,{once:true});
                     fallback = setTimeout(release,PENDING_VIEW_DESTROY_MS);
                 });