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.

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "jellytau"
-version = "0.9.0"
+version = "0.9.1"
 description = "A cross-platform Jellyfin client"
 authors = ["Duncan Tourolle <duncan@tourolle.paris>"]
 license = "MIT"