Improve media placeholders, avatar caching, and jumbo emoji layout.

Reserve image/video box size from info.w/h, fade in over blurhash blobs, cache dimensions/blurhashes and authenticated media blobs so avatars don't refetch every remount, and throttle TitleBar/DM reorder during sync catchup.

src/app/components/media/media.css.ts

@@ -5,8 +5,11 @@ export const Image = style([
   DefaultReset,
   {
     display: 'block',
+    width: '100%',
+    height: '100%',
     maxWidth: '100%',
     maxHeight: '100%',
+    objectFit: 'cover',
     borderRadius: 'inherit',
     imageRendering: 'auto',
     backfaceVisibility: 'hidden',
@@ -18,7 +21,10 @@ export const Video = style([
   DefaultReset,
   {
     display: 'block',
+    width: '100%',
+    height: '100%',
     maxWidth: '100%',
     maxHeight: '100%',
+    objectFit: 'cover',
   },
 ]);