fn_notify_applog_err collapses all 404s into one signature bucket

Signature SQL left(COALESCE(NULLIF(errorMessage,''), detail->>'digest', action), 500) falls through to literal 'action' string for page_not_found/nav rows (no errorMessage, no detail.digest) — every 404 across every route buckets identically, so alert/dedup-by-signature misreports a new 404 on an unrelated route as a recurrence. Fleet-wide (pluto discovery via nw-venus-cc relay, confirmed byte-identical in venus db/migrations/applied/applog-notify-error-trigger.sql and mars). Fix: key page_not_found/nav signatures off route/path instead of action, or carry URL in notify payload. Dispatched to db-venus-cc, Class-A (trigger/schema), audit-venus-ca pre-ping required.