feat(ECR-013A): Admin RBAC 实现并 Closed

角色权限、RequirePermission、/me permissions 与 migration 000015；
Reviewer Approve → Closed。Next：ECR-013B Contract Definition。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/migrations/000015_admin_rbac.down.sql

@@ -0,0 +1,4 @@
+UPDATE admin_accounts SET role_id = NULL WHERE role_id IS NOT NULL;
+ALTER TABLE admin_accounts DROP COLUMN IF EXISTS role_id;
+DROP TABLE IF EXISTS admin_role_permissions;
+DROP TABLE IF EXISTS admin_roles;