Fix task duplication: add single/multi-instance support with UI configuration and stop all running instances (#2837)

* Initial plan

* Stop running tasks before starting new scheduled instance

Co-authored-by: whyour <22700758+whyour@users.noreply.github.com>

* Add multi-instance support and fix stop to kill all running instances

- Add allow_multiple_instances field to Crontab model (default: 0 for single instance)
- Add validation for new field in commonCronSchema
- Add getAllPids and killAllTasks utility functions
- Update stop method to kill ALL running instances of a task
- Update runCron to respect allow_multiple_instances config
- Backward compatible: defaults to single instance mode

Co-authored-by: whyour <22700758+whyour@users.noreply.github.com>

* Add UI support for allow_multiple_instances configuration

- Add allow_multiple_instances field to ICrontab interface
- Add instance mode selector in task creation/edit modal
- Add translations for instance mode in Chinese and English
- Default to single instance mode for backward compatibility

Co-authored-by: whyour <22700758+whyour@users.noreply.github.com>

* Add allow_multiple_instances column migration and optimize db.ts

- Add allow_multiple_instances column to Crontabs table migration
- Refactor migration code to use data-driven approach
- Replace 11 individual try-catch blocks with single loop
- Improve code maintainability and readability

Co-authored-by: whyour <22700758+whyour@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: whyour <22700758+whyour@users.noreply.github.com>

back/validation/schedule.ts

@@ -64,7 +64,11 @@ export const commonCronSchema = {
         return value;
       }
 
-      if (!/^(?!.*(?:^|\/)\.{1,2}(?:\/|$))(?:\/)?(?:[\w.-]+\/)*[\w.-]+\/?$/.test(value)) {
+      if (
+        !/^(?!.*(?:^|\/)\.{1,2}(?:\/|$))(?:\/)?(?:[\w.-]+\/)*[\w.-]+\/?$/.test(
+          value,
+        )
+      ) {
         return helpers.error('string.pattern.base');
       }
       if (value.length > 100) {
@@ -77,4 +81,5 @@ export const commonCronSchema = {
       'string.max': '日志名称不能超过100个字符',
       'string.unsafePath': '绝对路径必须在日志目录内或使用 /dev/null',
     }),
+  allow_multiple_instances: Joi.number().optional().valid(0, 1),
 };