feat(player): persistent auto-advance + loop playback modes

Two saved-to-account playback settings on the player's prev/next bar (any queued
player — feed or playlist): Auto-advance (Off/Next/Prev/Random — what plays when a
video ends) and Loop (Off / One = repeat the current video / All = wrap the list
at its ends; a single-item list repeats). Stored in users.preferences
(playerAutoAdvance/playerLoop), read from the cached me + written via savePrefs so
they apply everywhere and survive reloads.

The feed's player queue is now the live filtered feed with the watch-state filter
NOT applied — marking the current video watched keeps it in the sequence (no
reindex/reload mid-play), while a hidden video still drops out. Removes the old
frozen-queue workaround and the boolean autoAdvance prop. i18n en/hu/de.

frontend/src/i18n/locales/de/player.json

@@ -4,6 +4,21 @@
   "back": "Zurück",
   "previous": "Vorheriges",
   "next": "Nächstes",
+  "autoAdvance": {
+    "label": "Auto",
+    "hint": "Was am Videoende folgt. Klicken zum Wechseln: Aus, Nächstes, Vorheriges, Zufall. In deinem Konto gespeichert.",
+    "off": "Aus",
+    "next": "Nächstes",
+    "prev": "Vorheriges",
+    "random": "Zufall"
+  },
+  "loop": {
+    "label": "Wiederholen",
+    "hint": "Aktuelles Video wiederholen (Eins), ganze Liste wiederholen (Alle) oder keines (Aus). In deinem Konto gespeichert.",
+    "off": "Aus",
+    "one": "Eins",
+    "all": "Alle"
+  },
   "close": "Schließen",
   "closeEsc": "Schließen (Esc)",
   "description": "Beschreibung",