changelog: group the #199 fragment and split it under the 300-char bound

The tree is grouped (fragments carry ### headings) and changelog-armed
caps each '- ' entry at 300 chars; the single 574-char bullet failed
both. Rewrite as three '### Changed' bullets.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

changelog.d/199.md

@@ -1 +1,13 @@
-- `labels` caller — the advisory sweep cron relaxes from `*/15` to hourly and the `issues:` trigger narrows to `[opened, closed]`, cutting how often a full-board reconcile is billed without changing what a sweep does or delaying any real state change past one cadence (#199). Events still carry every transition in seconds; the cron only backstops a forgotten handoff. Each caller trigger now carries a comment saying why it is subscribed, and the reconcile concurrency stays `cancel-in-progress: false` — cancelling a sweep mid-board is the race that guard exists to prevent.
+### Changed
+
+- `labels` — the advisory reconcile cron relaxes from `*/15` to hourly (#199).
+  Events still carry every state change in seconds; the cron only backstops a
+  forgotten handoff, so a full-board sweep is billed far less often without
+  delaying any real transition past one cadence.
+- `labels` — the caller's `issues:` trigger narrows to `[opened, closed]`
+  (#199), the two actions with reconcile behavior the cron cannot wait a
+  cadence for. The churn actions — labeled/unlabeled/assigned/unassigned/
+  edited/reopened — come off; the PR handoff wake is unaffected.
+- `labels` — each caller trigger now carries a comment saying why it is
+  subscribed, and reconcile keeps `cancel-in-progress: false` (#199) —
+  cancelling a sweep mid-board is the race that guard exists to prevent.