Migration baseline reset workflow

The suite no longer maintains dual migration tracks. Migration maintenance now uses a single canonical apps/*/migrations/ graph.

Baseline reset

Run a full baseline rebuild with:

.venv/bin/python manage.py migrations rebuild

Behavior:

1. Clears apps/*/migrations/ files except __init__.py.
2. Regenerates migrations into the canonical migrations/ modules.
3. Produces fresh initial migrations without branch-tag markers or parallel module routing.