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/en/player.json

@@ -4,6 +4,21 @@
   "back": "Back",
   "previous": "Previous",
   "next": "Next",
+  "autoAdvance": {
+    "label": "Auto",
+    "hint": "When a video ends, what plays next. Click to cycle Off, Next, Previous, Random. Saved to your account.",
+    "off": "Off",
+    "next": "Next",
+    "prev": "Previous",
+    "random": "Random"
+  },
+  "loop": {
+    "label": "Loop",
+    "hint": "Repeat the current video (One), loop the whole list (All), or neither (Off). Saved to your account.",
+    "off": "Off",
+    "one": "One",
+    "all": "All"
+  },
   "close": "Close",
   "closeEsc": "Close (Esc)",
   "description": "Description",