fix(rpast): serve interactive viewer at space root

Adds `GET /` to rpast routes. Without it, /rpast on a space subdomain
404'd because the sub-app had no root handler. Now matches the rNotes
pattern: bare domain → marketing landing, in-space URL → app shell with
<rpast-viewer>.

modules/rpast/mod.ts

@@ -12,11 +12,30 @@ import {
 	enumerateCreations, listCreationEnumerators, renderMarkwhen,
 } from '../../shared/markwhen';
 import { renderMarkwhenHtml } from '../../shared/markwhen/html-render';
+import { renderShell } from '../../server/shell';
+import { getModuleInfoList } from '../../shared/module';
 import { pastSchema } from './schemas';
 import { renderLanding } from './landing';
 
 const routes = new Hono();
 
+// GET / — marketing landing on bare domain, interactive viewer in a space.
+routes.get('/', c => {
+	const space = c.req.param('space') || 'demo';
+	if (!space || space === 'rpast.online') {
+		return c.html(renderLanding());
+	}
+	return c.html(renderShell({
+		title: `${space} — rPast | rSpace`,
+		moduleId: 'rpast',
+		spaceSlug: space,
+		modules: getModuleInfoList(),
+		theme: 'dark',
+		body: `<rpast-viewer space="${space}" style="height:calc(100vh - 52px);display:block"></rpast-viewer>`,
+		scripts: `<script type="module" src="/modules/rpast/rpast-viewer.js?v=1"></script>`,
+	}));
+});
+
 routes.get('/api/modules', c => {
 	return c.json(listCreationEnumerators().map(e => ({
 		module: e.module, label: e.label, icon: e.icon, color: e.color,