test: pin unit-suite timezone to UTC for deterministic date assertions

Date-formatting tests using toLocaleDateString rendered in the runner's local timezone, so assertions on specific dates only passed in UTC (as CI runs). Contributors east of UTC (e.g. UTC+12) saw off-by-one failures, e.g. CreditsTile rendering "Feb 21" instead of "Feb 20" for a noon-UTC renewal date.

vite.config.mts

@@ -706,6 +706,9 @@ export default defineConfig({
   test: {
     globals: true,
     environment: 'happy-dom',
+    // Pin the timezone so date-formatting assertions are deterministic
+    // regardless of the contributor's local timezone (CI runs in UTC).
+    env: { TZ: 'UTC' },
     setupFiles: ['./vitest.setup.ts'],
     retry: process.env.CI ? 2 : 0,
     include: [