feat(db): add Better-Auth schema tables (GRO-118)

Add user, session, account, and verification tables required by
Better-Auth's Drizzle adapter. Add nullable userId FK on staff to
link business identity to auth identity. Fix test fixtures and
factory to include the new column.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/__tests__/groomerIsolation.test.ts

@@ -15,6 +15,7 @@ import type { StaffRow } from "../middleware/rbac.js";
 const MANAGER: StaffRow = {
   id: "staff-manager-id",
   oidcSub: "oidc-manager-sub",
+  userId: null,
   role: "manager",
   name: "Manager McManager",
   email: "manager@example.com",

apps/api/src/__tests__/petPhotos.test.ts

@@ -7,6 +7,7 @@ import type { AppEnv, StaffRow } from "../middleware/rbac.js";
 const MANAGER: StaffRow = {
   id: "staff-manager-id",
   oidcSub: "oidc-manager-sub",
+  userId: null,
   role: "manager",
   name: "Manager McManager",
   email: "manager@example.com",

apps/api/src/__tests__/rbac.test.ts

@@ -8,6 +8,7 @@ import type { AppEnv, StaffRow } from "../middleware/rbac.js";
 const MANAGER: StaffRow = {
   id: "staff-manager-id",
   oidcSub: "oidc-manager-sub",
+  userId: null,
   role: "manager",
   name: "Manager McManager",
   email: "manager@example.com",