feat: complete Phase 0 Enterprise IAM

src/db/migrations/postgres/0006_create_role_permissions.sql

@@ -0,0 +1,7 @@
+CREATE TABLE IF NOT EXISTS role_permissions (
+    role_id       TEXT NOT NULL REFERENCES roles(id) ON DELETE CASCADE,
+    permission_id TEXT NOT NULL REFERENCES permissions(id) ON DELETE CASCADE,
+    PRIMARY KEY (role_id, permission_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_role_permissions_role ON role_permissions(role_id);