feat: add read-only M0 research ledger

[Pigbibi]

Summary

• add closed source-snapshot and M0 ledger schemas for research-only advisory hypotheses
• validate authority, no-order state, freshness, and provenance digests
• deduplicate exact source/subject copies and fail closed on inconsistent collisions
• surface cross-horizon conflicts as read-only console diagnostics

Safety

• no QPK selector import or strategy mapping
• no platform configuration, runtime target, scheduler, worker dispatch, credential, or UI mutation
• output is a bounded ledger for research review only

Validation

• python -m unittest tests.test_m0_research_ledger passed locally: 5 tests
• Python compile and diff checks passed
• GitHub CI will provide full repository regression coverage