Phase 2b preflight: cite the reliability addendum

[AMBRA7592]

Summary

• add the binding 2026-07-19 reliability-corpus addendum path alongside the existing pre-registration path
• emit both paths in the rendered Tier-2 report and as machine-readable manifest metadata
• factor manifest assembly into a pure helper and pin the entire synthetic manifest shape

Verification

• bare Python: 39 tests, 36 pass and 3 optional schema skips
• jsonschema 4.23.0: all 39 tests pass
• default disagreement to soft-labels to resolution artifacts are byte-identical to main d7f0c99
• importing run_study loads neither pyarrow nor pandas
• scope is exactly reports/mhs/run_study.py and test_claims.py

Boundary

Metadata-only hardening. Phase 2b remains halted: no parquet import, network access, structural preflight, outcome computation, report, or manifest occurred.