feat(authz): add database-backed PermissionStore

Adds dbPermissionStore/ensureAuthzTables/authzMigrationSql, backed by
_wrn_authz_assignment and _wrn_authz_grant tables, plus a ./db subpath
export. Passes the identical 19-test store-conformance suite the memory
adapter passes, including tenant-scope isolation.

tsconfig.json

@@ -32,6 +32,7 @@
       "@wrnexus/jwt": ["./packages/jwt/src/index.ts"],
       "@wrnexus/oauth": ["./packages/oauth/src/index.ts"],
       "@wrnexus/authz": ["./packages/authz/src/index.ts"],
+      "@wrnexus/authz/db": ["./packages/authz/src/db.ts"],
       "@wrnexus/helpers": ["./packages/helpers/src/index.ts"],
       "@wrnexus/encryption": ["./packages/encryption/src/index.ts"],
       "@wrnexus/pubsub": ["./packages/pubsub/src/index.ts"],