feat: 新增现场日历并将四类日历的起止地改为选填，以支持现场派车记录。

docs/sql/migrations/2026-10-30-dispatch-calendar-site-kind.sql

@@ -0,0 +1,18 @@
+-- 手工派车日历增加 site（现场日历）。仅更新 COMMENT，无结构变更。
+-- MySQL 5.7 / utf8mb4。可重复执行。
+SET NAMES utf8mb4;
+
+SET @col_exists = (
+  SELECT COUNT(*) FROM information_schema.COLUMNS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'pl_dispatch_calendar'
+    AND COLUMN_NAME = 'calendar_kind'
+);
+SET @ddl = IF(
+  @col_exists = 1,
+  'ALTER TABLE `pl_dispatch_calendar` MODIFY COLUMN `calendar_kind` varchar(16) NOT NULL DEFAULT ''acid'' COMMENT ''日历类型：acid酸派车 alkali碱派车 other其他 site现场''',
+  'SELECT 1'
+);
+PREPARE stmt FROM @ddl;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;