fix: restore auto-update registration broken by interval refactor

The "improve updater registration" refactor introduced two regressions in
the service mixin that disable auto-update for every service:

- initAutoUpdate() returned early when `interval > 0` and only called
  register() when the interval was 0, i.e. the guard was inverted: a valid
  interval skipped registration, and a disabled one registered with 0.
- getUpdateInterval() now resolves the interval into a local `interval`
  variable (supporting `updateIntervalMs` and the deprecated keys), but the
  service-specific branch still parsed `this.item.updateInterval`. Setting
  `updateIntervalMs` left that key undefined, so it returned 0 (disabled).

Register when `interval > 0`, and parse the resolved `interval` value.

src/mixins/service.js

@@ -90,7 +90,7 @@ export default {
       }
 
       const interval = this.getUpdateInterval();
-      if (interval > 0) {
+      if (interval <= 0) {
         return;
       }
       updateScheduler.register(this, interval, this.autoUpdateMethod);
@@ -128,7 +128,7 @@ export default {
 
       // Use service-specific interval if defined
       if (interval) {
-        return parseInt(this.item.updateInterval, 10) || 0;
+        return parseInt(interval, 10) || 0;
       }
 
       // Use global auto-update configuration