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.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "jellytau",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "description": "A cross-platform Jellyfin client built with Tauri, SvelteKit and Rust.",
   "author": "Duncan Tourolle <duncan@tourolle.paris>",
   "license": "MIT",