Production backbone: Supabase auth, RLS and billing foundation
Imported from GitHub issue El-SaMa/oma#82 by @El-SaMa.
Mirrors Hollahoop card: https://hollahoop.app/oma-portal/feedback/feature-requests/p/ba5e6206-c7ed-4dfd-a379-6889d152e51c
Scope:
- Supabase Auth + memberships for org/role resolution.
- Write RLS for org-scoped app tables.
- Credit ledger primitives for AI metering.
- Audit logging for destructive or billable actions.