fix: reuse frontend build artifact in e2e instead of rebuilding

The e2e job was running a full Vite build on the same runner as the
backend + Postgres, causing OOM. Now:
- Frontend job uploads dist/ as an artifact
- E2E job depends on frontend, downloads the artifact
- Playwright webServer skips build in CI, just runs preview
- Locally still builds as before

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/playwright.config.ts

@@ -38,10 +38,12 @@ export default defineConfig({
       },
     },
     {
-      command: 'NODE_OPTIONS="--max-old-space-size=4096" npm run build && npm run preview -- --host 127.0.0.1 --port 4173',
+      command: process.env.CI
+        ? 'npm run preview -- --host 127.0.0.1 --port 4173'
+        : 'NODE_OPTIONS="--max-old-space-size=4096" npm run build && npm run preview -- --host 127.0.0.1 --port 4173',
       url: frontendBaseUrl,
       reuseExistingServer: !process.env.CI,
-      timeout: 180_000,
+      timeout: 120_000,
       env: {
         ...process.env,
         VITE_API_URL: apiOrigin,