[grade=pending] fix: eliminate CPU waste from duplicate workflows, self-updater crash loop, and aggressive polling

- Remove duplicate WorkflowEngine instantiation (was created in both app.js
  and server.js, causing every periodic workflow to fire twice)
- Fix self-updater _isNewer() crash loop: same-version different-commit was
  treated as 'update available', then crashed on undefined tarball path.
  Now only triggers on actual version bumps
- Increase container stats interval from 10s to 30s
- Increase health check interval from 30s to 60s
- Add disk cleanup debounce (skip if last cleanup < 30 min ago)
- Remove redundant disk-space-monitor from server.js (already in app.js)
- 69/69 tests pass

dashcaddy-api/src/app.js

@@ -460,7 +460,7 @@ async function createApp() {
   // Initialize config drift detector
   const driftDetector = new ConfigDriftDetector(ctx);
   ctx.driftDetector = driftDetector;
-  driftDetector.startPolling(300000); // 5 min
+  driftDetector.startPolling(600000); // 10 min (was 5 min — docker inspect per container is CPU heavy)
   log.info('app', 'Config drift detector initialized');
 
   // Initialize SSL monitor
@@ -472,7 +472,7 @@ async function createApp() {
   // Initialize disk space monitor (disk budget + auto-cleanup)
   const diskSpaceMonitor = new DiskSpaceMonitor({ log, config: ctx.siteConfig });
   ctx.diskSpaceMonitor = diskSpaceMonitor;
-  diskSpaceMonitor.start(600000); // 10 min
+  diskSpaceMonitor.start(1800000); // 30 min (was 10 min — docker system df is CPU/IO heavy)
   log.info('app', 'Disk space monitor initialized', { budgetGB: diskSpaceMonitor.getConfig().diskBudgetGB });
 
   // Initialize DNS propagation checker
@@ -1105,7 +1105,7 @@ async function createApp() {
   app.use('/api', notFoundHandler);
   app.use(errorMiddleware);
 
-  return { app, log, config: config.siteConfig, licenseManager };
+  return { app, log, config: config.siteConfig, licenseManager, workflowEngine: ctx.workflowEngine };
 }
 
 module.exports = { createApp };