Block B complete: d124-transit-seed tooling + full D-124 NetBox import ...

Operator chose "write the seeder". netbox/d124-transit-seed.py (NEW) + harness
(21/21, incl. a cross-file consistency check so the seeded role/container can't
drift from dc-rack-mgmt-import's required ROLE_SLUG/CONTAINER) -- mirrors
d115-office-carve (NB client, sandbox gate, WAF UA, dry-by-default). Seeds ONLY
the transit role + the 172.31.0.0/24 UNSCOPED container (mirrors edge's /16).

Ran on the apex (gated, dry-run-verified, token server-side, sandbox-only):
seed -> role transit (id=30) + 172.31.0.0/24 (id=137); then dc-rack-mgmt-import
placed 172.31.0.0/30 (transit, vr1-dc0) + 10.12.8.2/22 (rack, dns=vvr1-dc0),
matching the vr1_dc0_rack_* tfvars. Full D-124/edge-WAN IPAM now in the apex.

changelog/ledger/readiness updated (Blocks A+B DONE).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ck6xh3jWQi5b3Su8Dx1LEH