docs: v0.19.1 — AGENTS.md documents enforced CI gate + auto-merge

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Changelog
 
+## v0.19.1 — 2026-09-19 18:48
+- AGENTS.md: document that CI-green is enforced on master by branch protection (required status check) and that merges use auto-merge (`merge_when_checks_succeed`) so PRs merge automatically once CI passes
+
 ## v0.19.0 — 2026-09-19 18:05
 - **Auto-slow to 1× when all planes have landed (ISS-011).** When the last plane in flight lands, the sim slows down on its own so an idle fleet doesn't sit at 1000×. Server-side and authoritative: `tickOnce` (`lib/sim/engine.ts`) now remembers how many planes `deliverPackages` finalized during a tick, and when ≥1 plane landed this tick AND no plane remains with status `'flying'` AND the sim is not paused, it persists `timeScale = 1` on the same `sim_state` write as the clock — so the UI slider reflects it on the very next snapshot (no API or OpenAPI change: timeScale is still set via the existing `POST /api/sim`, and `clampTimeScale` semantics are untouched since 1 is a valid ladder value)
 - **Arrival-triggered, not idle-enforced.** The trigger fires only on the tick that processes a landing — a grounded fleet at high scale with no flight ever happening is left alone (this keeps the existing slider e2e in `panes.spec.ts` green: it sets 1000× and expects the server to confirm it while nothing is flying). Paused state is untouched: while paused no landings are processed, so a paused sim never auto-slows