perf(build): measure the homepage and fix optimizePackageImports

/ is the highest-traffic route but was missing from both the public-route
instrumentation and the JS size budgets, so a payload regression there could
never fail the build. It is now wrapped in withPublicPagePerformance and
budgeted alongside the other public routes.

optimizePackageImports listed date-fns, which is not a dependency (a no-op),
while omitting the barrel-heavy packages that are actually imported: motion,
@dnd-kit/core, @dnd-kit/sortable and @tanstack/react-virtual.

next.config.ts

@@ -158,7 +158,15 @@ const nextConfig: NextConfig = {
 	},
 
 	experimental: {
-		optimizePackageImports: ["lucide-react", "date-fns"],
+		// Barrel-heavy packages: without this every import pulls the whole
+		// module graph into the chunk that first touches it.
+		optimizePackageImports: [
+			"lucide-react",
+			"motion",
+			"@dnd-kit/core",
+			"@dnd-kit/sortable",
+			"@tanstack/react-virtual",
+		],
 		useTypeScriptCli: true,
 		hideLogsAfterAbort: true,
 	},