Let each install pick its app icon

Settings > General gets an App icon (super admin): one of the seven
stones, or an uploaded image with the picked stone as a top-left corner
mark (inside a round launcher's crop, clear of the browser's badge),
previewed in both launcher crops before saving.

Uploads are decoded and cropped to a stored square (no SVG); the set is
drawn into DATA_DIR/install-icon/<version>/ and served publicly and
immutable. The manifest, head icon links and push notifications point at
it; the ember stone keeps the stock icons. The generator shares the icon
renderer.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/dict/push-dict.ts

@@ -10,6 +10,11 @@ export type PushPayload = {
     url: string;
     tag: string;
     requireInteraction?: boolean;
+    /**
+     * The install's own icon (`deliverToUser` fills it in); the worker
+     * falls back to the stock one.
+     */
+    icon?: string;
 };
 
 /**