feat(launcher): ship default brand assets

Solid-fill placeholders for the empty-state background (1920×1080) and
the zero-teaser hero fallback (800×450). Brand-refresh slice can drop
both files in without touching code. Loaded once on init via
engine.asset.load_texture (launcher's own sandbox).

manifest.module

@@ -1,6 +1,6 @@
 {
   "id": "lib-management.launcher",
-  "version": "0.3.1",
+  "version": "0.3.2",
   "kind": "module",
   "api": "^0.1",
   "ci_frames": 10,