fix(home): restart the hero banner timer on a manual change

The rotation interval was installed once when the banner mounted and never
touched again, so a swipe, arrow or dot tap inherited whatever was left of the
running countdown — swiping 5.5s into a 6s interval moved the banner on half a
second later.

The timer moves into heroRotation.ts as a small restartable object so it can be
unit-tested, and every manual navigation path restarts it from that moment.
Verified red-first: with restart() reverted to leave a running timer alone, the
regression test fails.

Release 0.9.1.

CHANGELOG.md

@@ -9,6 +9,20 @@ generated trace matrix lives in [docs/traceability.md](docs/traceability.md).
 For how long each fixed defect had been shipping before it was found, see
 [docs/defect-windows.md](docs/defect-windows.md).
 
+## v0.9.1
+
+A one-line fix to the home screen, released on its own because it is the kind of
+small wrongness you notice every time.
+
+### 🐛 Fixes
+
+- **Swiping the hero banner now buys you a full six seconds.** The rotation
+  timer was started once when the banner appeared and then left alone, so a
+  swipe, arrow or dot tap inherited whatever was left of the running countdown
+  — swipe five and a half seconds in and the banner moved on half a second
+  later, before you had read the title. Any manual change now restarts the
+  countdown from that moment. (UR-034 → DR-038)
+
 ## v0.9.0
 
 An audit release. One new setting you asked for, two naming bugs that only ever