[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/server.js

@@ -21,7 +21,7 @@ process.on('uncaughtException', (error) => {
 (async () => {
   try {
     // Create and configure Express app
-    const { app, log, config, licenseManager } = await createApp();
+    const { app, log, config, licenseManager, workflowEngine: appWorkflowEngine } = await createApp();
     
     // Load license
     await licenseManager.load();
@@ -112,11 +112,13 @@ process.on('uncaughtException', (error) => {
       try { logDigest = require('./src/security/log-digest'); } catch { /* optional */ }
       try { bundledWorkflows = require('./src/recipes/bundled-workflows'); } catch { /* optional */ }
 
-      // Initialize workflow engine if bundled-workflows is available
-      // NOTE: createApp() already initializes the workflow engine in src/app.js
-      // This block is kept for backward compat with entry points that don't use createApp()
-      let workflowEngine = null;
-      if (bundledWorkflows) {
+      // Reuse the workflow engine created by createApp() to avoid duplicate
+      // scheduled jobs (DC-CPU: two WorkflowEngine instances each scheduled
+      // health-check-on-interval, causing every periodic workflow to fire
+      // twice and double the polling load). Only create one if createApp()
+      // didn't (e.g. legacy entry points without docker).
+      let workflowEngine = appWorkflowEngine || null;
+      if (!workflowEngine && bundledWorkflows) {
         try {
           const { fetchT } = require('./src/utils/http');
           const { WorkflowEngine } = bundledWorkflows;
@@ -134,7 +136,7 @@ process.on('uncaughtException', (error) => {
             servicesStateManager
           };
           workflowEngine = new WorkflowEngine(workflowCtx);
-          log.info('server', 'Workflow engine initialized');
+          log.info('server', 'Workflow engine initialized (fallback)');
         } catch (err) {
           log.error('server', 'Workflow engine failed to initialize', { error: err.message });
         }