error-tier toast/error-shown rows would page despite mig 074 mute (warn-only scope)

Surfaced from VENUS-325 alert-rail measurement (coder-mars-cc, 2026-07-30): mig 074's friction mute (mig 074) is scoped to level=warn AND category=toast only. Mars's error/fatal DB-trigger branch has NO category test at all, so an error-tier toast/error-shown row would page today if one occurred — a live exposure with a quiet history, not a closed issue. category=toast/error-shown is mars's LARGEST admitted alert class (695 rows/29 routes), currently all warn-tier (last row 2026-06-06, looks fixed upstream by a level change) but the gate does not enforce that. Decide: widen mig 074's mute to cover error-tier toast rows too, or confirm error-tier toast is intentionally pageable and accept the exposure.