fix(rdesign): add publicWrite flag to unblock POST requests

The write-method middleware was returning 403 for POST /api/design-agent
because the module lacked publicWrite: true.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/rdesign/mod.ts

@@ -302,6 +302,7 @@ export const designModule: RSpaceModule = {
 	icon: "\u{1f3af}",
 	description: "AI-powered DTP workspace — text in, design out",
 	scoping: { defaultScope: 'global', userConfigurable: false },
+	publicWrite: true,
 	routes,
 	landingPage: renderDesignLanding,
 	feeds: [