Replaces the v1 two-key declaration with the schema_version 2 form per
mosaic-brain docs/plans/2026-08-23_repo-structure-declaration.md section
1.3 (spec of record @ brain main 515bcbab): flow, canonical_remote,
canonical_clone, worktree_root, and transitional worktree_policy
(orchestrator-precreated until the J3/#1174 amendment). Validated by the
wave-1 validator: OK in managed mode with launch-equivalent anchors;
fail-closed on absent anchors per spec 1.2a interim; display mode warns
and passes. Docs-only, exactly one file.
code-be-01
