docs: nightly research report 2026-03-13

Task registry metadata regression (436 claimed vs 274 actual),
missing verification_modes/use_case_category fields, ANSWER_PATH
scope correction (122 files, not 55), judge dimension doc mismatch,
broken EVALUATION_PIPELINE.md cross-reference, and correction to
Mar 11 report re: sanitize_secrets integration.

Author: sjarmak