feat(settings): click own avatar in profile preview to view fullscreen

Lightbox was previously a file-private component inside AttachmentImage
(used for enlarging chat image attachments). Extracted to a standalone
components/Lightbox.tsx so other surfaces can reuse the same dialog
without duplicating Esc/backdrop/body-overflow plumbing.

In SettingsPage's profile live-preview, the round avatar overlapping the
banner is now wrapped in a transparent button that opens the Lightbox
with the full-resolution avatar URL on click. Cursor switches to
zoom-in. Disabled when the user only has the initial-letter placeholder
(nothing meaningful to enlarge). Native button chrome (border, padding,
button-face background) is reset to keep the avatar circle's appearance
unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/pages/SettingsPage.tsx

@@ -33,6 +33,7 @@ import {
   uploadBannerBlob,
 } from '../lib/bannerUpload';
 import { ImageCropDialog } from '../components/ImageCropDialog';
+import { Lightbox } from '../components/Lightbox';
 import { devLocalSecretStore } from '../lib/secretStore';
 import {
   getPttSettings,
@@ -799,6 +800,9 @@ function ProfileVisualsControls({ patchProfile, busy }: AvatarControlsProps) {
   // ratios.
   const [cropFile, setCropFile] = useState<File | null>(null);
   const [cropKind, setCropKind] = useState<'avatar' | 'banner' | null>(null);
+  // Lightbox toggle for the avatar live-preview. Clicking the in-page
+  // avatar opens a fullscreen view; clicking outside / Esc dismisses.
+  const [avatarPreviewOpen, setAvatarPreviewOpen] = useState(false);
 
   const userId = profile?.userId;
   const avatarUrl = profile?.avatarUrl ?? null;
@@ -930,11 +934,33 @@ function ProfileVisualsControls({ patchProfile, busy }: AvatarControlsProps) {
           className="relative z-10 flex items-end gap-3 px-4 pb-3"
           style={{ marginTop: '-2rem' }}
         >
-          <Avatar
-            url={avatarUrl}
-            displayName={displayName}
-            className="h-16 w-16 rounded-full text-2xl ring-4 ring-surface-3"
-          />
+          <button
+            type="button"
+            onClick={() => {
+              if (avatarUrl) setAvatarPreviewOpen(true);
+            }}
+            // Disabled when there's no uploaded avatar — clicking the
+            // generated-initial placeholder would open an empty lightbox.
+            disabled={!avatarUrl}
+            aria-label={
+              avatarUrl
+                ? t('app:settings.avatar_preview', { defaultValue: 'Profilbild vergrößern' })
+                : undefined
+            }
+            // appearance-none + reset border/bg/padding so the native
+            // button chrome (outset border, button-face background, 1px
+            // padding) doesn't draw a box around the avatar circle.
+            className={
+              'appearance-none border-0 bg-transparent p-0 rounded-full focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/40 ' +
+              (avatarUrl ? 'cursor-zoom-in' : 'cursor-default')
+            }
+          >
+            <Avatar
+              url={avatarUrl}
+              displayName={displayName}
+              className="h-16 w-16 rounded-full text-2xl ring-4 ring-surface-3"
+            />
+          </button>
           <div className="min-w-0 flex-1 pb-1">
             <div className="truncate text-sm font-semibold text-fg">
               {displayName ?? '—'}
@@ -1061,6 +1087,9 @@ function ProfileVisualsControls({ patchProfile, busy }: AvatarControlsProps) {
         }}
         onClose={closeCropDialog}
       />
+      {avatarPreviewOpen && avatarUrl && (
+        <Lightbox url={avatarUrl} onClose={() => setAvatarPreviewOpen(false)} />
+      )}
     </div>
   );
 }