Replace video player with a fully custom fake-fullscreen HUD

Single fullscreen player state everywhere (desktop/Android/iOS/feed) instead
of the old modal-vs-native-fullscreen split, with custom controls: draggable
timeline with buffered range, dynamically-escalating skip buttons (double-tap
zones too), per-video format switching, favorites, PiP with auto-PiP on
backgrounding, volume swipe, TikTok-style HUD auto-hide, and swipe-down/
back-button/close-button dismissal. Reels feed reuses the same skip/format/
PiP logic via the new customPlayer.js shared module.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/js/ui.js

@@ -612,7 +612,6 @@ App.ui = App.ui || {};
     App.ui.bindGlobalHandlers = function() {
         window.toggleDrawer = App.ui.toggleDrawer;
         window.closeDrawers = App.ui.closeDrawers;
-        window.closePlayer = App.player.close;
         window.handleSearch = App.videos.handleSearch;
 
         const modeToggleBtn = document.getElementById('mode-toggle-btn');