feat(frontend): add brand kit management UI and project binding

Add a brand kit domain model, repository, and dedicated page/route for
managing brand kits, plus a BrandKitSelector used on the home page and
canvas workspace. Home project creation and the workspace can attach a
brand kit to a project, with new i18n strings and a side-nav entry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/ui/App.tsx

@@ -7,6 +7,7 @@ import { readRoute, type AppRoute } from "@/application/route";
 import { designGateway } from "@/infrastructure/designGateway";
 import { httpStatusOf } from "@/infrastructure/userMessages";
 import { BrandMark } from "@/ui/components/BrandMark";
+import { BrandKitRoutePage } from "@/ui/pages/BrandKitRoutePage";
 import { CanvasWorkspace } from "@/ui/pages/CanvasWorkspace";
 import { HomePage } from "@/ui/pages/HomePage";
 import { NotFoundPage } from "@/ui/pages/NotFoundPage";
@@ -46,6 +47,7 @@ export function App() {
   if (route.name === "project") return <CanvasWorkspace projectId={route.id} />;
   if (route.name === "share") return <SharedCanvasRoute shareId={route.id} />;
   if (route.name === "projects") return <ProjectsRoutePage />;
+  if (route.name === "brandKit") return <BrandKitRoutePage />;
   if (route.name === "notFound") return <NotFoundPage />;
   return <HomePage />;
 }