feat(keys): j/k walk the feed, s finds the search box, g jumps to a module

A feed card cost ~10 Tab stops, so the tenth card sat ~135 Tabs from the top of the page, and the
only keyboard focus ring (a 60% accent outline on the thumbnail) all but vanished on the dark glass.
First slice of the E11 keyboard layer (S4a); Home, Plex and the tables follow in S4b/S4c.

- `lib/listNav`: one window listener over every registered list, walked in document order. `j`/`k`
  step item to item (on into the next list — owner decision D4), the arrows move around a grid, Enter
  clicks the item's own `data-nav-open` element, so it opens exactly like a click. An item root is
  never a Tab stop: it gets `tabindex=-1` only while the keyboard is on it, and keeps it until the next
  item takes it, so the player's focus restore lands back on the card. The first `j` takes the first
  card you can see, not the top of the list.
- `VirtualGrid` takes part with `keyboardNav` (column count + scrolling an unmounted row in);
  `VirtualFeed` turns it on, so the feed, the library and the channel page all have it.
- Keymap: two-step sequences (`g h`) whose pending step belongs to the scope that started it; the
  page-level scopes (`page`, `search`, `list`) are quiet while a layer that owns the keyboard is open,
  enforced in `dispatch`. A test pins the owner's rule that none of them needs a modifier on the
  Hungarian layout.
- `g h/f/c/p/x/n/m/d/s/,` jump to a module this account can reach; `s` focuses the header search box
  and selects the old query; Escape in it hands the keyboard back to the page (Plex's typeahead spends
  its first Escape on its panel).
- Hover popovers are passive layers: an open tooltip still takes Escape first but no longer silences
  the page keys.
- Focus ring (owner decision D2 = B): solid 2px accent around the whole item; the app-wide button/
  link/row ring goes from 60% to solid too. The item keeps a transparent resting outline because the
  video card transitions `all` — without it every `j` flashed a 3px white ring (measured in Chrome).
- Help sheet: the new keys, in a fixed order after the surface's own; a `g` chord only for a reachable
  module; opened over a player or dialog it leaves out the page-level keys and the context-menu key,
  which nothing can reach there (the latter pre-existing since E10).
- CLAUDE.md: a canonical-patterns row for list/grid keys (`useListNav` + `navItemAttrs` +
  `data-nav-open`, not a private arrow-key handler).

frontend/src/components/VideoCard.nav.dom.test.tsx

@@ -0,0 +1,89 @@
+// @vitest-environment jsdom
+//
+// E11 S4: the video card's half of keyboard navigation (`lib/listNav`). Every layout's ROOT carries the
+// list index — that is the element `j`/`k` focus and ring — and the title link is the card's `open`
+// element, so Enter on a selected card runs the very click a mouse would: the in-app player.
+import { beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import { cleanup, render, screen } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+vi.mock("react-i18next", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("react-i18next")>()),
+  useTranslation: () => ({ t: (key: string) => key, i18n: { language: "en" } }),
+}));
+vi.mock("./NavigationProvider", () => ({
+  useNavigationActions: () => ({ openChannel: vi.fn() }),
+}));
+
+import VideoCard from "./VideoCard";
+import type { Video } from "../lib/api";
+import type { FeedView } from "../lib/feedView";
+
+beforeAll(() => {
+  class Stub {
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+    takeRecords() {
+      return [];
+    }
+  }
+  globalThis.ResizeObserver ??= Stub as unknown as typeof ResizeObserver;
+  globalThis.IntersectionObserver ??= Stub as unknown as typeof IntersectionObserver;
+});
+
+const video = {
+  id: "abc123",
+  title: "Cicada 3301",
+  channel_id: "UCsXVk37bltHxD1rDPwtNM8Q",
+  channel_title: "LEMMiNO",
+  status: "new",
+  saved: false,
+  position_seconds: 0,
+  duration_seconds: 1200,
+  published_at: "2026-01-01T00:00:00Z",
+  watch_url: "https://www.youtube.com/watch?v=abc123",
+  thumbnail_url: "",
+} as unknown as Video;
+
+beforeEach(cleanup);
+
+function renderCard(view: FeedView, navIndex?: number, onOpen = vi.fn()) {
+  render(
+    <QueryClientProvider client={new QueryClient()}>
+      <VideoCard
+        video={video}
+        view={view}
+        width={0}
+        navIndex={navIndex}
+        onState={() => {}}
+        onToggleSave={() => {}}
+        onOpen={onOpen}
+      />
+    </QueryClientProvider>,
+  );
+  return onOpen;
+}
+
+// One per layout FAMILY: the stacked card, the thumbnailed row, the one-line row — three roots.
+const VIEWS: FeedView[] = ["cards", "rows", "rowsCompact"];
+
+describe("VideoCard — keyboard navigation hooks", () => {
+  for (const view of VIEWS) {
+    it(`puts the list index on the ${view} root and opens in-app from the title`, () => {
+      const onOpen = renderCard(view, 7);
+      const root = screen.getByTestId("video-card");
+      expect(root.getAttribute("data-nav-index")).toBe("7");
+      const open = root.querySelectorAll("[data-nav-open]");
+      expect(open).toHaveLength(1);
+      expect(open[0]!.textContent).toBe("Cicada 3301");
+      (open[0] as HTMLElement).click();
+      expect(onOpen).toHaveBeenCalledWith(video);
+    });
+  }
+
+  it("carries no index outside a navigable list (Home's rails)", () => {
+    renderCard("cards");
+    expect(screen.getByTestId("video-card").hasAttribute("data-nav-index")).toBe(false);
+  });
+});