fix(jellyfin): subtitle timing, resume progress, and overlay sync

- Add per-stream subtitle delay persistence and auto timeline-offset correction
- Strip server-selected subtitle stream from mpv load URL; suppress plugin subtitle rearm and auto-start during app-managed preload
- Fix resume position lost when mpv resets on stop; use last known position for final progress/stopped reports
- Keep Play vs Resume distinct to avoid early seek race on normal play
- Fix discovery resume when remote play sends StartPositionTicks=0 despite saved progress
- Deduplicate show/hide overlay commands using recorded visibility state
- Rewrite docs-site Jellyfin page around cast-to-device UX

src/main/runtime/overlay-visibility-actions.ts

@@ -1,4 +1,5 @@
 export function createSetVisibleOverlayVisibleHandler(deps: {
+  getVisibleOverlayVisible?: () => boolean;
   setVisibleOverlayVisibleCore: (options: {
     visible: boolean;
     setVisibleOverlayVisibleState: (visible: boolean) => void;
@@ -9,6 +10,9 @@ export function createSetVisibleOverlayVisibleHandler(deps: {
   onVisibleOverlayEnabled?: () => void;
 }) {
   return (visible: boolean): void => {
+    if (deps.getVisibleOverlayVisible?.() === visible) {
+      return;
+    }
     if (visible) {
       deps.onVisibleOverlayEnabled?.();
     }