Fix frontend CI pipeline OOM kills and test timeouts

- Set memory limit to 2048MiB for the "Run frontend tests" step
  (node:24-alpine was OOM killed at the default 1Gi)
- Set memory limit to 2048MiB for the "Build frontend image" kaniko
  step (also OOM killed at 1Gi)
- Increase vitest testTimeout to 30s (CI runner is ~75x slower than
  local dev; tests were timing out at the default 5s)

frontend/vitest.config.ts

@@ -15,5 +15,6 @@ export default defineConfig({
     setupFiles: ['./src/__tests__/setup.ts'],
     css: false,
     include: ['src/**/*.test.{ts,tsx}'],
+    testTimeout: 30000,
   },
 });