fix(shell): hide subnav bar on rspace canvas page

The rspace module's outputPaths caused renderModuleSubNav to render an
unwanted "rspace | Canvases" bar across the canvas. Skip subnav for the
root rspace module since the canvas has its own chrome.

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

server/shell.ts

@@ -1356,6 +1356,7 @@ const SUBNAV_CSS = `
 
 /** Build the module sub-nav bar from outputPaths + subPageInfos. */
 function renderModuleSubNav(moduleId: string, spaceSlug: string, modules: ModuleInfo[]): string {
+	if (moduleId === 'rspace') return ''; // canvas page has its own chrome
 	const mod = modules.find(m => m.id === moduleId);
 	if (!mod) return '';