fix(rpc): empty icon in transient install entry to avoid broken-image flicker

create_installing_entry hardcoded /assets/img/app-icons/<id>.png for
every new install. About half the app icons ship as .svg or .webp
(lnd.svg, vaultwarden.webp, bitcoin-knots.webp, mempool.webp), so the
browser 404s on the wrong extension and renders the default broken-image
glyph for the 10-30s window before the scanner refreshes with real
manifest data.

Send empty icon. The frontend's icon computed in AppCard.vue falls
through to curatedMap which has correct extensions for bundled apps,
and handleImageError still guards any remaining misses with a
placeholder SVG.

core/archipelago/src/api/rpc/package/progress.rs

@@ -69,7 +69,11 @@ fn create_installing_entry(package_id: &str) -> PackageDataEntry {
         static_files: StaticFiles {
             license: String::new(),
             instructions: String::new(),
-            icon: format!("/assets/img/app-icons/{}.png", package_id),
+            // Empty icon: hardcoding `<id>.png` is wrong for apps that use
+            // `.svg` or `.webp` assets and produces a broken-image flicker.
+            // The frontend's `icon` computed falls through to the curated
+            // map which has correct extensions for known apps.
+            icon: String::new(),
         },
         manifest: Manifest {
             id: package_id.to_string(),