feat: run jobs on instance creation when run_on_create is enabled

Jobs with run_on_create=true in their config fire automatically
after a new instance is created. Runs fire-and-forget so they don't
delay the 201 response. Option exposed as a checkbox in each job's
detail panel.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/routes.js

@@ -5,7 +5,7 @@ import {
   getConfig, setConfig, getJobs, getJob, updateJob, getJobRuns,
   getAllJobs, getAllJobRuns, importJobs,
 } from './db.js';
-import { runJob, restartJobs } from './jobs.js';
+import { runJob, restartJobs, runJobsOnCreate } from './jobs.js';
 
 export const router = Router();
 
@@ -102,6 +102,7 @@ router.post('/instances', (req, res) => {
     createInstance(data);
     const created = getInstance(data.vmid);
     res.status(201).json(created);
+    runJobsOnCreate().catch(() => {});
   } catch (e) {
     handleDbError('POST /api/instances', e, res);
   }