[follow-up to #337 + #338 + #339 + #341] Cluster-24 migration ledger needs to land first — multiple PRs collide on V5

[ohdearquant]

ADR-015 ledger:

• V5: ADR-043 embedding_pipeline_extensions
• V6: ADR-046 event_sourced_proposals_index
• V7: ADR-041 event_observations_and_session_id
• V8: ADR-022 events_namespace_ts_id_idx

PRs already stamping V5/V6/V7 for unrelated work:

• [ADR-001/008] Entity Kind and Type Contract (cluster-01) #337 c01: stamps V5 add_entity_type_to_entities (codex CRIT)
• [ADR-002/004/029/038] Edge ontology, lifecycle, bulk link (cluster-03) #338 c03: stamps V5 edge_lifecycle_and_target_backend (codex Blocker)
• [ADR-013/014] Note kind, storage, curation (cluster-04) #339 c04: stamps V7 note_storage_curation (codex Critical)
• [ADR-004/009/014] Event observable + provenance (cluster-06) #341 c06: collapses V6/V7/V8 into single V5 (codex Critical)

Cluster-24 (schema-migration-ledger) is supposed to harmonize the ledger before downstream clusters stamp. It hasn't been built yet. Each cluster picked its own V-number locally.

Fix sequence:

1. Build cluster-24 first: amend ADR-015 to extend the ledger with slots for c01/c03/c04/c06.
2. After cluster-24 merges, rebase c01/c03/c04/c06 onto it and re-stamp.
3. Update tests asserting migration versions.

Reference: codex CRIT #2 on #337; identical findings on #338/#339/#341.

[ohdearquant]

Resolved by PR #349 — cluster-24 schema migration ledger landed (c24), and all V5+ collisions were renumbered cleanly. No remaining cross-cluster migration conflicts on main.