[plan] Operator credentials roster UX fixes at scale

_Automatically composed from the parent epic at dispatch time._

Split along the architecture's seams into 8 children: stored facts/indexes → {stamps, keyset roster API} → {pager/search/health UI, owner typeahead, tree, bulk} → dev walk. Done-checks tightened (A3 expiry, phone legibility, O(1) bulk, skip-scan property test). Dev reach still unverified, so the 500-row dev check may fall back to the slot API test. Memory: none applied.