Auto-remove memories after sustained irrelevance #347
Description
Problem
Noise quadrant removal requires manual apply-proposal approval — a human bottleneck that's never exercised. Noise grows indefinitely.
Desired behavior
After a memory accumulates N irrelevant marks with zero relevant marks (e.g., 10 irrelevant, 0 relevant), auto-delete with backup to memories/.backup/. No manual approval needed.
Dependencies
Requires #343 (irrelevant_count tracking).
Priority
Medium effort, medium impact.
See investigation doc for full analysis.