feat(db): add migrations for RBAC, diagnostic, messaging, attendance, leave, invitation codes

- 0011: RBAC role flags and seed data

- 0012: diagnostic grade_id

- 0013: message recall

- 0014: message templates

- 0015: group messages and message reports/blocks

- 0016: invitation codes

- 0017: draft device sync

- 0018: attendance status reason

- 0019: attendance warning thresholds

- 0020: leave requests

- 0021: attendance period

drizzle/0015_group_messages.sql

@@ -0,0 +1,3 @@
+-- P2-2: 群组消息（教师→全班家长，fan-out on write）
+ALTER TABLE `messages` ADD COLUMN `group_message_id` varchar(128);
+CREATE INDEX `messages_group_message_idx` ON `messages`(`group_message_id`);