chore: add concurrency to speed tests

Author: jorgemoya

unlighthouse.config.ts

@@ -15,11 +15,6 @@ export default {
     // outliers across all discovered pages (no explicit warm-up step needed).
     samples: 3,
   },
-  puppeteerClusterOptions: {
-    // Limit to one concurrent Lighthouse instance to mitigate hardware-throttling
-    // false positives that previously caused us to disable the performance category.
-    maxConcurrency: 1,
-  },
   lighthouseOptions: {
     // Performance re-enabled — hardware throttling concerns are mitigated by
     // maxConcurrency: 1 (no concurrent runs) and samples: 3 (median smoothing).