GET /history SELECTed latest estimates of ALL users -> cross-pilot leak.
Adds trade_in_estimates.created_by (migration 083), populated from
X-Authenticated-User on estimate creation. /history now: non-admin forced
to own rows (legacy NULL rows excluded); admin sees all or ?account=<user>;
401 if header missing, 403 if user not in roles.yaml. _empty_estimate rows
also tagged. tests/test_history_scope.py (5 cases) + estimator regression green.
Closes#656