feat(plex): on-screen ±10s skip buttons flanking play/pause (E6 S3)

Add discoverable rewind-10 / forward-10 controls to the Plex player control
bar, flanking play/pause (D5-A). New Skip10 glyph: an outline circular arrow
with a centred '10', deliberately distinct from the episode-level
SkipBack/SkipForward and from Restart's plain RotateCcw. Reuses seekTo; mirrors
the keyboard ←/→ (seekStep=10). i18n HU/EN aria-labels.

frontend/src/components/plexPlayerControls.tsx

@@ -1,6 +1,49 @@
 import { type ReactNode } from "react";
 import { RotateCcw } from "lucide-react";
 
+// ±10s skip glyph: an outline circular arrow with a "10" in the centre — the YouTube/Plex-native
+// muscle-memory shape. Deliberately distinct from the episode-level SkipBack/SkipForward (double
+// triangles) and from Restart's plain RotateCcw. The arrowhead is an L-corner at the arc's open end,
+// the same construction lucide uses for RotateCcw/RotateCw, so it sits consistently in the bar.
+export function Skip10({ dir }: { dir: "back" | "forward" }) {
+  const back = dir === "back";
+  return (
+    <svg
+      viewBox="0 0 24 24"
+      fill="none"
+      stroke="currentColor"
+      strokeWidth={2}
+      strokeLinecap="round"
+      strokeLinejoin="round"
+      className="w-6 h-6"
+      aria-hidden="true"
+    >
+      {back ? (
+        <>
+          <path d="M4 8.5 A8 8 0 1 1 4 12" />
+          <path d="M4 8.5 L4 4 M4 8.5 L8.5 8.5" />
+        </>
+      ) : (
+        <>
+          <path d="M20 8.5 A8 8 0 1 0 20 12" />
+          <path d="M20 8.5 L20 4 M20 8.5 L15.5 8.5" />
+        </>
+      )}
+      <text
+        x="12"
+        y="14.5"
+        textAnchor="middle"
+        fontSize="8"
+        fontWeight={700}
+        fill="currentColor"
+        stroke="none"
+      >
+        10
+      </text>
+    </svg>
+  );
+}
+
 // --- settings-panel building blocks ------------------------------------------------------------
 export function PanelHead({ children }: { children: ReactNode }) {
   return (