fix(plex): seek tooltip tracks cursor under scale; tidy the tuning menu

- The seek-bar hover tooltip positioned itself with a px `left` derived
  from the scaled getBoundingClientRect, so inside the transform:scale
  player it got re-scaled and drifted right of the cursor (only 0 was
  right). Position it by fraction (% of the bar) instead — it now sits
  under the cursor at any point, like the volume tooltip already did.
- The tuning (gear) menu tabs wrapped to two lines at the +25% scale.
  Widen the menu, keep tab labels on one line (whitespace-nowrap), and
  shorten the labels: "Sync offset" → "Offsets", "Subtitle style" →
  "Subtitles" (all three languages).

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

@@ -126,14 +126,14 @@
       "fineSeek": "Fine seek"
     },
     "settings": "Settings",
-    "sync": "Sync offset",
+    "sync": "Offsets",
     "subOffset": "Subtitle delay",
     "audioOffset": "Audio delay",
     "playback": "Playback",
     "seekStep": "Seek step",
     "fineSeek": "Fine seek (Ctrl)",
     "autoHide": "Auto-hide controls",
-    "subStyle": "Subtitle style",
+    "subStyle": "Subtitles",
     "subSize": "Text size",
     "subPos": "Position",
     "subColor": "Text color",