feat: adaptive progressive image loading for photo viewer (#26636)

* 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.

* fix: don't partially render images in firefox

* add passive loading indicator to asset-viewer

---------

Co-authored-by: Alex <alex.tran1502@gmail.com>

web/src/lib/actions/zoom-image.ts

@@ -2,7 +2,11 @@ import { assetViewerManager } from '$lib/managers/asset-viewer-manager.svelte';
 import { createZoomImageWheel } from '@zoom-image/core';
 
 export const zoomImageAction = (node: HTMLElement, options?: { disabled?: boolean }) => {
-  const zoomInstance = createZoomImageWheel(node, { maxZoom: 10, initialState: assetViewerManager.zoomState });
+  const zoomInstance = createZoomImageWheel(node, {
+    maxZoom: 10,
+    initialState: assetViewerManager.zoomState,
+    zoomTarget: null,
+  });
 
   const unsubscribes = [
     assetViewerManager.on({ ZoomChange: (state) => zoomInstance.setState(state) }),