feat(schedules): auto-update stacks by Stack Label (#1717)

* feat(schedules): auto-update stacks by Stack Label

Add a reusable selector_type/selector_value on scheduled tasks so admins
can schedule image updates against live Stack Label membership across the
fleet or one node, reusing fleet label resolution and the existing
auto-update orchestrator.

* fix(image-updates): sanitize auto-update execute failure logs

Use a static format string and sanitizeForLog so CodeQL no longer
flags user-controlled stack names and error text in the execute catch.

* fix(ui): space Scope label from fleet/node segmented control

Match the Schedule row layout so the inline SegmentedControl no longer
sits flush against the Scope label.

* fix(ui): remove redundant wrapper around Scope segmented control

backend/src/__tests__/dashboard-routes.test.ts

@@ -113,7 +113,7 @@ describe('GET /api/dashboard/configuration', () => {
       last_error: null,
       prune_targets: null,
       target_services: null,
-      prune_label_filter: null,
+      prune_label_filter: null, selector_type: null, selector_value: null,
     };
     const idA = db.createScheduledTask({
       ...baseTask,