fix(ui): unknown app ids fall back to the A mark, not a 404 png guess

resolveAppIcon's final arm guessed /assets/img/app-icons/<id>.png — strfry
404'd live. DEFAULT_APP_ICON already existed; the chain now ends on it.

Co-Authored-By: Claude <noreply@anthropic.com>

neode-ui/src/views/apps/__tests__/appsConfig.test.ts

@@ -1,7 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import { ref } from 'vue'
 import { PackageState, type PackageDataEntry } from '@/types/api'
-import { canLaunch, filterEntriesForTab, hasFrontendUi, isServiceContainer, isServicePackage, isWebsitePackage, launchBlockedReason, resolveAppIcon, useCategoriesWithApps } from '../appsConfig'
+import { canLaunch, filterEntriesForTab, hasFrontendUi, isServiceContainer, isServicePackage, isWebsitePackage, launchBlockedReason, resolveAppIcon, useCategoriesWithApps, DEFAULT_APP_ICON } from '../appsConfig'
 
 function makePkg(id: string, title: string, category: string): PackageDataEntry {
   return {
@@ -82,6 +82,13 @@ describe('appsConfig service filtering', () => {
     expect(resolveAppIcon('gitea', pkg)).toBe('/assets/img/app-icons/gitea.svg')
   })
 
+  it('an unmapped id gets the A mark, not a guessed png that 404s', () => {
+    // strfry 404'd live on 2026-08-07: no curated entry, no fallback entry,
+    // no service prefix — the old `${id}.png` guess produced a broken tile.
+    const pkg = makePkg('strfry', 'strfry', 'nostr')
+    expect(resolveAppIcon('strfry', pkg)).toBe(DEFAULT_APP_ICON)
+  })
+
   it('classifies an unknown app by whether its manifest declares a UI (#45)', () => {
     // Headless: a LAN address but no declared UI → Website.
     const headless = makePkg('some-backend', 'Some Backend', 'other')

neode-ui/src/views/apps/appsConfig.ts

@@ -249,7 +249,9 @@ export function resolveAppIcon(id: string, pkg: PackageDataEntry, curatedIcon?:
     curatedIcon ||
     APP_ICON_FALLBACKS[id] ||
     serviceParentIcon(id) ||
-    `/assets/img/app-icons/${id}.png`
+    // Never guess `${id}.png` — an unmapped id 404s (strfry did, 2026-08-07).
+    // The A mark is the honest unknown-app tile.
+    DEFAULT_APP_ICON
   )
 }