- Detect API-level errors (quota exceeded, invalid URL) in response JSON
and store in scan_error instead of silently writing zeros
- Show scan error message on the performance card when present
- Show "No performance data — configure PAGESPEED_API_KEY" when all
scores are 0 and no error was recorded
- Add accessibility and best practices scores to performance card
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>