fix(web): resolve Firefox thumbnail hover lines and inconsistent focus outlines

- Add transform: translateZ(0) to thumbnail gradient overlay to force
  GPU compositing, eliminating horizontal rendering artifacts in Firefox
  on hover (fixes #28338).

- Remove the global input:focus-visible { outline: none !important }
  override in app.css. The blanket rule hid keyboard focus indicators
  from all native inputs while @immich/ui buttons kept their own
  focus-visible outline, producing an inconsistent and inaccessible
  admin/settings experience (fixes #19498).

web/src/app.css

@@ -153,10 +153,12 @@
     background-color: black;
   }
 
-  input:focus-visible {
+  /* Removed global input:focus-visible override to ensure consistent,
+     accessible focus outlines across all pages (fixes #19498). */
+  /* input:focus-visible {
     outline-offset: 0px !important;
     outline: none !important;
-  }
+  } */
 
   .text-white-shadow {
     text-shadow: 0 1px 2px rgba(0, 0, 0, 0.8);

web/src/lib/components/assets/thumbnail/Thumbnail.svelte

@@ -313,6 +313,7 @@
               'absolute size-full bg-linear-to-b from-black/25 via-[transparent_25%] opacity-0 transition-opacity group-hover:opacity-100',
               { 'rounded-xl group-focus-visible:rounded-lg': selected },
             ]}
+            style="transform: translateZ(0);"
           ></div>
         {/if}