refactor: hook dependencies name everything the hooks read

The 12 react-hooks/exhaustive-deps warnings the gate let through:
- ShareDialog and YearFilter built a fresh [] per render while their query loaded, so their
  memos recomputed on every render; they share one empty list now.
- VideoEditor's drag effect called a seek/moveBoundary recreated each render; both are stable
  callbacks in its deps.
- WizardProvider re-checks onboarding on exactly the fields it reads (not the me object, whose
  60 s refetch would reopen a closed wizard).
- Channels, Feed and PlexPlayer list the stable values they already used.
- The player's keydown effect is bound once on purpose (its helpers read refs): said so, with a
  disable, as the codebase's other deliberate sites do.
- dialogFocus and the YouTube player's cleanup read refs React may already have let go of; they
  use what they captured when the effect ran.

frontend/src/components/VideoEditor.tsx

@@ -130,10 +130,13 @@ export default function VideoEditor({ job, onClose }: { job: DownloadJob; onClos
     const v = videoRef.current;
     if (v) setCurrent(v.currentTime);
   };
-  const seek = (s: number) => {
-    const v = videoRef.current;
-    if (v) v.currentTime = Math.max(0, Math.min(duration, s));
-  };
+  const seek = useCallback(
+    (s: number) => {
+      const v = videoRef.current;
+      if (v) v.currentTime = Math.max(0, Math.min(duration, s));
+    },
+    [duration],
+  );
   const playPause = () => {
     const v = videoRef.current;
     if (!v) return;
@@ -154,18 +157,21 @@ export default function VideoEditor({ job, onClose }: { job: DownloadJob; onClos
       return next;
     });
   };
-  const moveBoundary = (bi: number, time: number) =>
-    setSegments((segs) => {
-      if (creating.current || bi < 0 || bi >= segs.length - 1) return segs;
-      // bi is in [0, length-2] here, so bi and bi+1 both index existing segments.
-      const lo = segs[bi]!.start + MIN_SEG;
-      const hi = segs[bi + 1]!.end - MIN_SEG;
-      const tt = Math.max(lo, Math.min(hi, time));
-      const copy = [...segs];
-      copy[bi] = { ...copy[bi]!, end: tt };
-      copy[bi + 1] = { ...copy[bi + 1]!, start: tt };
-      return copy;
-    });
+  const moveBoundary = useCallback(
+    (bi: number, time: number) =>
+      setSegments((segs) => {
+        if (creating.current || bi < 0 || bi >= segs.length - 1) return segs;
+        // bi is in [0, length-2] here, so bi and bi+1 both index existing segments.
+        const lo = segs[bi]!.start + MIN_SEG;
+        const hi = segs[bi + 1]!.end - MIN_SEG;
+        const tt = Math.max(lo, Math.min(hi, time));
+        const copy = [...segs];
+        copy[bi] = { ...copy[bi]!, end: tt };
+        copy[bi + 1] = { ...copy[bi + 1]!, start: tt };
+        return copy;
+      }),
+    [],
+  );
   const deleteBoundary = (bi: number) =>
     setSegments((segs) => {
       if (creating.current || segs.length < 2) return segs;
@@ -205,7 +211,7 @@ export default function VideoEditor({ job, onClose }: { job: DownloadJob; onClos
       window.removeEventListener("pointermove", move);
       window.removeEventListener("pointerup", up);
     };
-  }, [drag, timeAt]);
+  }, [drag, timeAt, seek, moveBoundary]);
 
   // --- crop drag ---
   const overlayRef = useRef<HTMLDivElement>(null);