Enterprise tenancy: add organizations, teams, RBAC, and SCIM

[tcballard]

Why

Workspaces and virtual keys are a useful data-plane base, but larger deployments need governed identity lifecycle and delegated administration.

Scope

• Add organization and team hierarchy without weakening workspace isolation.
• Define roles and least-privilege permissions for operators, billing, policy, audit, and key administration.
• Map validated OIDC claims to governed roles.
• Add SCIM provisioning, suspension, group mapping, and deprovisioning.
• Keep operator identity separate from inference credentials.
• Audit all administrative mutations.

Acceptance criteria

• Authorization is enforced server-side on every administrative operation.
• Deprovisioned users and groups lose access within a bounded interval.
• Role changes cannot broaden model, privacy, or budget policy implicitly.
• Cross-organization reads and mutations fail in adversarial tests.
• No provider credentials are exposed through identity administration.

Parent: #146

Invariant

The scored model decision remains offline, deterministic, keyless, and explainable.