test(analysis): assert Cancelled event is published; correct cron-test rationale (0.87.21)

0.87.13 followup. The Cancelled publish had no asserting test —
mechanical revert of the publish block shipped green. New sqlx test
subscribes before spawn, drives SlowDispatcher into flight, cancels,
asserts both Started and Cancelled frames with breadcrumb fields.
Mutation-confirmed.

Also corrects: cron-test rationale comment (inverted unlock-axis),
Cancelled docstring (self-contradicting clear-triggers sentence).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.87.20",
+  "version": "0.87.21",
   "private": true,
   "type": "module",
   "scripts": {