fix(player): marks give way to newer lists, Watch later items mark, and auto-advance has its own glyphs

A session's marks are weighed per field against when each page of a never-refetched list was read:
a page read before the mark (a Show more / Load more on its way) takes it, one read after keeps the
server's word. The live search lays them over its rows too, not only the related list.

Items of the built-in Watch later list ARE the bookmark, so adding, removing and moving them go
through features/video/videoWrites and mark the video; the contract test covers those writes and
catches a write that is named without being called on the spot.

The player's watched toggle follows a mark confirmed elsewhere since it opened (the related row's
menu, a notice's Undo); Restart on the related row after a description link goes back to it.
The file viewer tells the help sheet its keys wait under a layer; refusalReason replaces the last
two open-coded reads.

Auto-advance wears list glyphs of its own (the skip arrows are Previous / Next beside it), and the
auto-advance and loop cycles are `lit`, not toggles: no aria-pressed, the name says the mode. Both
places render from one list of controls, so the docked tooltips name the mode too. The English cap
message and admin hint quote "Show more"; the hint says refunds are limited.

frontend/src/modules/files/FilePreview.tsx

@@ -11,7 +11,7 @@ import {
 } from "lucide-react";
 import { api, HttpError, type FilePreviewKind, type LibraryFile } from "../../lib/api";
 import { formatBytes } from "../../lib/format";
-import { dispatch, useKeyScope } from "../../lib/keymap";
+import { dispatch, setScopeCoveredProbe, useKeyScope } from "../../lib/keymap";
 import { useLayer } from "../../lib/layerStack";
 import { qk } from "../../lib/queryKeys";
 import { jobTitle } from "../../features/downloads/downloadTitle";
@@ -85,6 +85,12 @@ export default function FilePreview({
   // child first, so it sits just ABOVE the dialog's layer: the dialog is never topmost, and Escape is
   // this layer's to take — passive, so the dialog keeps its Tab trap.
   const layer = useLayer(!!file, onClose, { passive: true });
+  // …and the help sheet opened over that layer must not list them (keymap `setScopeCoveredProbe`).
+  const coveredNow = useEffectEvent(() => layer.blockingAbove());
+  useEffect(() => {
+    setScopeCoveredProbe("fileViewer", () => coveredNow());
+    return () => setScopeCoveredProbe("fileViewer", null);
+  }, []);
   const onKey = useEffectEvent((e: KeyboardEvent) => {
     if (layer.blockingAbove()) return;
     // The text, scrolled sideways by its arrows: a line wider than the stage is read that way.