plugins: a splash is part of a plugin, like its icon

assets/splash.png is discovered by presence, published by the same copy that
already took the whole assets directory, and carried on DiscoveredPlugin beside
icon.

The platform draws no splash — a plugin has no launch. It is carried because the
plugin repository is where a product's artwork lives now, and the phone app that
fronts the same product needs somewhere to read it from that is not a designer's
folder. The pair is the point: the icon is a reduction of the splash's world,
and keeping them together is what stops them drifting.

Publishing no longer gates on the icon alone, which left a plugin shipping only
a splash serving nothing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/plugins/manifest.ts

@@ -240,6 +240,18 @@ export type DiscoveredPlugin = {
    * naming one outside that set silently renders a neutral box.
    */
   icon: string | null;
+  /**
+   * `assets/splash.png` — the app's launch scene, published beside the icon.
+   *
+   * The platform itself draws no splash; a plugin has no launch. It is carried because the plugin
+   * repository is where a product's artwork lives now, and the mobile app that fronts the same
+   * product needs somewhere to read it from that is not a designer's folder. Presence is the
+   * declaration, exactly as with the icon.
+   *
+   * The pair is deliberate: `assets/icon.png` is a reduction of `assets/splash.png`'s world, and
+   * keeping them in one place is what stops the two drifting apart.
+   */
+  splash: string | null;
   /** `api/router.ts` — a backend router, mounted at `mountPrefix`. */
   api: string | null;
   /** `db/schema.ts` — tables, pushed on install. Every name must be prefixed `<appName>_`. */