Add startup benchmark harness

Author: mjc

package.json

@@ -44,6 +44,7 @@
     "typecheck": "turbo run typecheck",
     "lint": "oxlint --report-unused-disable-directives",
     "test": "turbo run test",
+    "bench:startup": "bun scripts/bench-startup.js",
     "test:desktop-smoke": "turbo run smoke-test --filter=@t3tools/desktop",
     "fmt": "oxfmt",
     "fmt:check": "oxfmt --check",