style(home): color the success-rate meter by rate

The home overview bar stayed brown down to 80%. Color it continuously from red through yellow to green so it follows the measured success rate.

tests/homeOverviewCards.test.tsx

@@ -0,0 +1,34 @@
+import { expect, it } from 'bun:test';
+import { renderToStaticMarkup } from 'react-dom/server';
+import { I18nProvider } from '../src/i18n';
+import { HomeOverviewCards } from '../src/pages/HomeOverviewCards';
+import { requestRateColor } from '../src/services/authFileRequests';
+import type { HomeOverviewSnapshot } from '../src/services/homeOverview';
+
+const snapshot = (rate: number | null): HomeOverviewSnapshot => ({
+  usage: {
+    totalRequests: rate == null ? 0 : 100,
+    successCount: rate ?? 0,
+    failureCount: rate == null ? 0 : 100 - rate,
+    canceledCount: 0,
+    successRate: rate,
+  },
+  credentials: null,
+  providerKeys: null,
+  models: null,
+  errors: {},
+});
+
+const render = (rate: number | null) => renderToStaticMarkup(
+  <I18nProvider>
+    <HomeOverviewCards snapshot={snapshot(rate)} loading={false} coreReady onRefresh={() => {}} />
+  </I18nProvider>,
+);
+
+it('colors the success meter continuously from red through yellow to green', () => {
+  expect(render(100)).toContain(`--stat-color:${requestRateColor(1)}`);
+  expect(render(50)).toContain(`--stat-color:${requestRateColor(0.5)}`);
+  expect(render(0)).toContain(`--stat-color:${requestRateColor(0)}`);
+  expect(render(95)).not.toContain('home-stat-card warning');
+  expect(render(null)).not.toContain('--stat-color');
+});