Implement PostgreSQL production store path

Add the PostgreSQL backend, migration and stopped-write transfer tools, lease-aware deployment manifests, tenancy declarations, and shared conformance coverage. Persist grouping mutations in durable stores and separate process liveness from database readiness.

pyproject.toml

@@ -17,6 +17,10 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
+postgres = [
+    "psycopg[binary]>=3.2,<4.0",
+    "psycopg-pool>=3.2,<4.0",
+]
 dev = [
     "pytest>=8.2,<9.0",
     "ruff>=0.6,<1.0",
@@ -24,6 +28,8 @@ dev = [
 
 [project.scripts]
 tenant-engine = "tenant_engine.main:main"
+tenant-engine-migrate = "tenant_engine.migrate:main"
+tenant-engine-transfer = "tenant_engine.transfer:main"
 
 [tool.setuptools.packages.find]
 where = ["src"]