GameCult theme, steward-grouped project rooms, preview base override

Adds the gamecult-theme (brand palette, softer radii, Ubuntu/Montserrat/Plex Mono),
makes it the default, hides the member drawer by default, defaults to bubble layout,
groups rooms by org.gamecult.steward in the space nav (collapsed on phones), and lets
CINNY_BASE set Vite's base for a sub-path preview build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

build.config.ts

@@ -1,3 +1,3 @@
 export default {
-  base: '/',
+  base: process.env.CINNY_BASE ?? '/',
 };