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/public-paths.test.ts

@@ -30,6 +30,7 @@ const plugin = (appName: string, unauthenticatedPaths?: string[], publisher = 'o
       ...(unauthenticatedPaths ? { unauthenticatedPaths } : {}),
     },
     icon: null,
+    splash: null,
     api: null,
     schema: null,
     sidecar: null,