fix: add --plugins.add analysisstorer to sitespeed.io args

analysisstorer is not in the default plugin set, so pageSummary JSON
files were never written. This plugin writes all message data to disk
(browsertime.pageSummary.json, coach.pageSummary.json, etc.) which
our parser reads to extract metrics.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

runner.js

@@ -21,7 +21,7 @@ export function runTest(job, onLine) {
       '--browser', job.browser,
       '-n', String(job.runs),
       '--outputFolder', outputFolder,
-      '--json',
+      '--plugins.add', 'analysisstorer', // not in default set — needed to write pageSummary JSON
       '--sustainable.enable',
       '--sustainable.useGreenWebHostingAPI',
       '--axe.enable',