make upload and metadata UI responsive on mobile.

Improve narrow-viewport layout for upload, About, and shell overflow; keep modal scroll without extra dismiss or a11y markup changes.

frontend/src/components/upload/ShareLinkField.vue

@@ -1,7 +1,7 @@
 <template>
     <label class="flex flex-col gap-1.5 text-xs">
         <span class="font-medium text-muted-foreground">{{ label }}</span>
-        <div class="flex gap-2">
+        <div class="flex flex-col gap-2 sm:flex-row">
             <input
                 type="text"
                 readonly
@@ -10,7 +10,7 @@
             />
             <button
                 type="button"
-                class="shrink-0 rounded-md border border-border px-3 py-2 text-xs font-medium transition-colors hover:bg-muted/60"
+                class="shrink-0 rounded-md border border-border px-3 py-2.5 text-xs font-medium transition-colors hover:bg-muted/60 sm:py-2"
                 @click="onCopyClick"
             >
                 {{ copied ? 'Copied' : 'Copy' }}