feat(plex): player polish — clock overlay, sub shadow, auto-skip, seekbar hover

- Wall clock is now a Clock settings tab: show/hide, 24h↔12h (am/pm), size, colour, and
  an optional date in two fixed styles (EN "08-JUL-2026 Wed" / HU "2026-JÚL-08 Sze").
- Subtitle text-shadow (blur strength + colour) in the Subtitle tab.
- Auto-skip intro/credits: per-user toggles + a shared 0–10s delay (default 5). Entering a
  marker whose auto-skip is on runs a countdown shown as a fill on the Skip button; on
  completion it skips (intro → marker end, credits → next item / binge). Esc/Backspace during
  the countdown cancels it and does NOT navigate back. 0s = immediate.
- Seekbar hover shows a timestamp tooltip that follows the cursor.
- i18n en/hu/de for the new strings.

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

@@ -138,7 +138,18 @@
     "subPos": "Position",
     "subColor": "Textfarbe",
     "subBg": "Hintergrund",
-    "subBgNone": "Keiner"
+    "subBgNone": "Keiner",
+    "clock": "Uhr",
+    "clockShow": "Uhr anzeigen",
+    "clock24h": "24-Stunden",
+    "clockSize": "Größe",
+    "clockColor": "Farbe",
+    "clockDate": "Datum anzeigen",
+    "subShadow": "Schatten",
+    "subShadowColor": "Schattenfarbe",
+    "autoSkipIntro": "Intro autom. überspringen",
+    "autoSkipCredits": "Abspann autom. überspringen",
+    "autoSkipDelay": "Auto-Skip-Verzögerung"
   },
   "info": {
     "title": "Medieninfo",