feat(web): adaptive progressive image loading for photo viewer

Replace ImageManager with a new AdaptiveImageLoader that progressively
loads images through quality tiers (thumbnail → preview → original).

New components and utilities:
- AdaptiveImage: layered image renderer with thumbhash, thumbnail,
  preview, and original layers with visibility managed by load state
- AdaptiveImageLoader: state machine driving the quality progression
  with per-quality callbacks and error handling
- ImageLayer/Image: low-level image elements with load/error lifecycle
- PreloadManager: preloads adjacent assets for instant navigation
- AlphaBackground/DelayedLoadingSpinner: loading state UI

Zoom is handled via a derived CSS transform applied to the content
wrapper in AdaptiveImage, with the zoom library (zoomTarget: null)
only tracking state without manipulating the DOM directly.

Also adds scaleToCover to container-utils and getAssetUrls to utils.

e2e/src/ui/specs/asset-viewer/broken-asset.e2e-spec.ts

@@ -64,7 +64,9 @@ test.describe('broken-asset responsiveness', () => {
 
   test('broken asset in main viewer shows icon and uses text-base', async ({ context, page }) => {
     await context.route(
-      (url) => url.pathname.includes(`/api/assets/${fixture.primaryAsset.id}/thumbnail`),
+      (url) =>
+        url.pathname.includes(`/api/assets/${fixture.primaryAsset.id}/thumbnail`) ||
+        url.pathname.includes(`/api/assets/${fixture.primaryAsset.id}/original`),
       async (route) => {
         return route.fulfill({ status: 404 });
       },
@@ -73,7 +75,7 @@ test.describe('broken-asset responsiveness', () => {
     await page.goto(`/photos/${fixture.primaryAsset.id}`);
     await page.waitForSelector('#immich-asset-viewer');
 
-    const viewerBrokenAsset = page.locator('#immich-asset-viewer #broken-asset [data-broken-asset]');
+    const viewerBrokenAsset = page.locator('[data-viewer-content] [data-broken-asset]').first();
     await expect(viewerBrokenAsset).toBeVisible();
 
     await expect(viewerBrokenAsset.locator('svg')).toBeVisible();