feat(web): face overlay hover UX and face editor zoom preservation

Change-Id: I7164305d7764bec54fa06b8738cd97fd6a6a6964

refactor(web): use asset metadata for face editor image dimensions instead of DOM

The face editor previously read naturalWidth/naturalHeight from the DOM
element via a $effect + load event listener. This was fragile on slow
hardware (ARM CI) because imgRef changes as AdaptiveImage progresses
through quality levels, and the DOM element's natural dimensions could
be 0 during transitions.

Now the face editor receives imageSize as a prop from the parent, derived
from the asset's metadata dimensions which are always available immediately.

Change-Id: Id4c3a59110feff4c50f429bbd744eac46a6a6964
Change-Id: I7164305d7764bec54fa06b8738cd97fd6a6a6964

web/src/lib/stores/face-edit.svelte.ts

@@ -1 +1,2 @@
 export const isFaceEditMode = $state({ value: false });
+export const isEditFacesPanelOpen = $state({ value: false });