feat: shard group messages by month

docs/sql/IM-用户账号编号序列表SQL.sql

@@ -0,0 +1,15 @@
+-- 在每个租户业务库执行。用于并发安全地生成 im_users.account_no。
+CREATE TABLE IF NOT EXISTS im_user_account_sequences (
+    id TINYINT UNSIGNED NOT NULL,
+    next_value INT UNSIGNED NOT NULL,
+    updated_at DATETIME(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3)
+        ON UPDATE CURRENT_TIMESTAMP(3),
+    PRIMARY KEY (id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
+
+-- 兼容已有用户数据，从当前最大账号编号继续递增，账号编号最小为 1000。
+INSERT INTO im_user_account_sequences (id, next_value)
+SELECT 1, GREATEST(COALESCE(MAX(account_no), 999), 999)
+FROM im_users
+ON DUPLICATE KEY UPDATE
+    next_value = GREATEST(next_value, VALUES(next_value));