test(performance): add a local pokédex benchmark and run it in CI

Measures the pokédex load against a local Supabase with a generated fixture, and
compares runs so a regression shows up as a number rather than a hunch. Wired
into test:ci and given its own job so the artifacts survive a failure.

scripts/performance/compare.mjs

@@ -0,0 +1,46 @@
+import { readFile } from 'node:fs/promises';
+const data = JSON.parse(await readFile(process.argv[2], 'utf8'));
+const warm = data.results.filter((row) => row.run === 'warm');
+const p75 = (values) => [...values].sort((a, b) => a - b)[Math.ceil(values.length * 0.75) - 1];
+const groups = [...new Set(warm.map((row) => `${row.fixture}/${row.navigation}`))];
+const paired = groups.map((group) => {
+	const rows = (host) =>
+		warm.filter((row) => `${row.fixture}/${row.navigation}` === group && row.host === host);
+	for (const host of ['netlify', 'cloudflare'])
+		if (rows(host).length < 30) throw new Error(`Insufficient ${host} warm samples for ${group}`);
+	return {
+		group,
+		netlify: p75(rows('netlify').map((row) => row.interactiveMs)),
+		cloudflare: p75(rows('cloudflare').map((row) => row.interactiveMs))
+	};
+});
+if (groups.length !== 4)
+	throw new Error(
+		'Expected national and scoped-form fixtures, each with direct and client navigation'
+	);
+const netlify = p75(warm.filter((row) => row.host === 'netlify').map((row) => row.interactiveMs));
+const cloudflare = p75(
+	warm.filter((row) => row.host === 'cloudflare').map((row) => row.interactiveMs)
+);
+const improvement = netlify - cloudflare;
+const passes =
+	improvement >= 200 &&
+	improvement / netlify >= 0.2 &&
+	paired.every((row) => row.cloudflare <= row.netlify * 1.1);
+console.log(
+	JSON.stringify(
+		{
+			overallP75: { netlify, cloudflare },
+			improvementMs: improvement,
+			improvementPercent: (100 * improvement) / netlify,
+			groups: paired,
+			performanceGatePassed: passes,
+			recommendation:
+				passes && data.compatibilityPassed && data.environment === 'deployed'
+					? 'Cloudflare qualifies for a migration proposal; review operating cost before cutover.'
+					: 'Retain Netlify: performance, deployed evidence or compatibility gate is unmet.'
+		},
+		null,
+		2
+	)
+);