Run 216 recovered 403s (merged fix) but still banned on a 429 at page 36
(deep pagination, backconnect conn-limit). Widen the 429 retry budget + one
reconnect on exhaustion in _fetch_serp_html, and make fetch_all_secondary skip
a blocked bucket and continue rather than aborting the run; only N consecutive
blocked buckets (real hard ban) re-raises. Preserves hard-ban detection.
