添加公告管理权限配置

- 新增 announcement:view 和 announcement:manage 权限
- 为超级管理员和运营角色添加公告管理权限
- 迁移文件：000007_add_announcement_permissions.sql

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/migrations/000007_add_announcement_permissions.sql

@@ -0,0 +1,19 @@
+-- 添加公告管理权限
+
+INSERT INTO permissions (code, name, resource, action) VALUES
+('announcement:view',    '查看公告',    'announcement',  'view'),
+('announcement:manage',  '管理公告',    'announcement',  'manage')
+ON DUPLICATE KEY UPDATE
+  name = VALUES(name),
+  resource = VALUES(resource),
+  action = VALUES(action);
+
+-- 为超级管理员添加公告权限
+INSERT IGNORE INTO role_permissions (role_id, permission_id)
+SELECT r.id, p.id FROM roles r CROSS JOIN permissions p
+WHERE r.code = 'super_admin' AND p.code IN ('announcement:view', 'announcement:manage');
+
+-- 为运营角色添加公告权限
+INSERT IGNORE INTO role_permissions (role_id, permission_id)
+SELECT r.id, p.id FROM roles r, permissions p
+WHERE r.code = 'ops' AND p.code IN ('announcement:view', 'announcement:manage');