TEN-WP-0002 T01-T03: service skeleton, domain model, storage layer

Python 3.12 + FastAPI, pyproject.toml + Makefile mirroring
qonto-assistant's exactly. src/tenant_engine/{domain,store,app,main}.py:

- domain.py: Tenant, CapabilityRole (PLTF/IAM/VEN/CUS), RoleGrant,
  PlanAssignment, create_role_grant() enforcing ADR-0014's invariants.
  Refinement made while implementing: platform_default grants are valid
  for trial-grouped tenants OR the reserved tenant:platform/tenant:coulomb
  tenants (their baseline roles were never purchased either) -- the task
  spec only named the trial case.
- store.py: TenantStore Protocol + InMemoryTenantStore, every mutation
  emits a DomainEvent per the boundary contract's Audit Correlation
  Contract.
- app.py/main.py: FastAPI factory + /health endpoint, verified live on
  127.0.0.1:8090.

29 tests passing, including non-exclusive role coexistence (CUS+VEN
simultaneously) and append-only revoke semantics.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/tenant_engine/main.py

@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+import uvicorn
+
+from tenant_engine.app import create_app
+
+
+def main() -> None:
+    uvicorn.run(create_app(), host="127.0.0.1", port=8090)
+
+
+if __name__ == "__main__":
+    main()