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.

scripts/performance-budgets.json

@@ -2,6 +2,11 @@
 	"schemaVersion": 1,
 	"mode": "enforce",
 	"routes": [
+		{
+			"route": "/",
+			"maxInitialRawBytes": 716800,
+			"maxInitialGzipBytes": 225280
+		},
 		{
 			"route": "/me",
 			"maxInitialRawBytes": 716800,