Real 404s hidden in alert-rail noise: /login x19, /practicas/<uuid> x36

Surfaced from VENUS-325 alert-rail measurement (coder-mars-cc, 2026-07-30): /login returned 404 nineteen times and one /practicas/<uuid> route was hammered with 404s 36 times, both real user-facing failures that were sitting invisible inside the alert rail's mixed navigation/404 noise bucket alongside scanner probes. Not an alerting item — investigate the app-side cause (broken link, stale bookmark/share, route regression) independent of the applog classifier work.