feat(canvas): fullscreen workspace outside the app shell

Move /projects/:id and its service detail route out of PlatformShell —
the project view now owns the entire viewport like Railway's canvas:
no sidebar, no global nav, just the slim project bar over the graph.
Service detail inherits the same chrome-free context with a breadcrumb
back to the canvas, and back/delete navigation preserves ?demo=1.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/features/service/pages/ServiceDetailPage.tsx

@@ -384,7 +384,7 @@ export function ServiceDetailPage() {
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['project-services', projectId] });
       queryClient.invalidateQueries({ queryKey: ['projects'] });
-      navigate(`/projects/${projectId}`);
+      navigate(isDemoMode ? `/projects/${projectId}?demo=1` : `/projects/${projectId}`);
     },
   });