chore: relocate backend into apps/api ahead of monorepo merge

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

apps/api/models/users/user_groups.attributes.js

@@ -0,0 +1,38 @@
+const excludeAttributes = [
+];
+
+const jsonbSchemas = {
+  // Add here
+};
+
+// Different exclude sets per role
+const adminExclude = [
+  ...excludeAttributes,
+  // admins can see audit fields, so nothing extra excluded
+];
+
+const userExclude = [
+  ...excludeAttributes,
+  // regular users cannot see audit trails
+  "created_by", "updated_by", "deleted_by",
+  "deleted_at",
+];
+
+const computedAttributes = [
+  {
+    key: "memberCount",
+    label: "Members",
+    type: "number",
+    order: 5,
+    literal: `(
+      SELECT CAST(COUNT(*) AS INTEGER)
+      FROM "user_group_members"
+      JOIN "users" ON "users"."user_id" = "user_group_members"."user_id"
+      WHERE "user_group_members"."group_id" = "UserGroup"."group_id"
+        AND "user_group_members"."deletedAt" IS NULL
+        AND "users"."deletedAt" IS NULL
+    )`,
+  },
+];
+
+module.exports = { excludeAttributes, adminExclude, userExclude, jsonbSchemas, computedAttributes };