fix(keys): epic-end review round 1 — Back, menus and dialogs keep the focus where it belongs

Deep-review of E11 (19 raised, 14 confirmed; 2 refuted, 3 latent test-hardening notes dropped).

- Back from a sub-view (a Plex show page, a Messages thread) restores the item it was opened from
  even when focus was still inside the view: the first attempt now waits one task, past the
  sub-view's own popstate listener (measured in Chrome: it left focus on <body>).
- The restore listener is installed at load, so the first Back after a reload finds it; a push
  cancels a restore still waiting for the last landing's lists.
- Navigating over an overlay asks it again, a render apart, while its entry stays: the Plex
  player peels one panel per Back step, so Shift+W over info + stats closed one panel and dropped
  the navigation.
- j/k: a native <button> item keeps its own Tab stop; landing twice on the same item no longer
  leaks its tabindex; after the focused item is removed (a hidden card) the next j goes on from
  its slot when that slot is on screen.
- An abandoned `g` no longer swallows a modifier chord (g, then Mod+K opened the browser search).
- A hover card above a dialog no longer switches its Tab trap off (player, Modal, wizard,
  Lightbox): new layerStack `anyBlockingLayerAbove`.
- "Manage views…" closes its menu before opening the dialog, through a shared `closeThenAct`
  that ActionMenu now uses too.
- Copy: the EN welcome says "Feed"; the EN unreachable reason no longer claims a change;
  stale comments about PlayerModal's scroll lock and dialog contract.

frontend/src/components/ui/Modal.dom.test.tsx

@@ -22,6 +22,7 @@ vi.mock("../../lib/history", () => ({ useBackToClose: () => {} }));
 
 import Modal from "./Modal";
 import { clearAll, notify } from "../../lib/notifications";
+import { pushLayer, removeLayer } from "../../lib/layerStack";
 
 // Fire a keydown on window (where Modal installs its handler), inside act.
 const press = (key: string, shiftKey = false) =>
@@ -93,6 +94,24 @@ describe("Modal focus trap (offsetParent stubbed 'visible')", () => {
     expect(document.activeElement).toBe(screen.getByText("beta"));
   });
 
+  // A tooltip or hover card open under a resting pointer is a (passive) layer above the dialog. It
+  // takes Escape first, but deferring the Tab trap to it let Shift+Tab walk out behind the scrim.
+  it("keeps trapping while only a hover card is open above it", () => {
+    render(
+      <Modal title="t" onClose={() => {}}>
+        <Body />
+      </Modal>,
+    );
+    const hover = pushLayer({ passive: true });
+    try {
+      screen.getByText("beta").focus(); // last
+      press("Tab");
+      expect(document.activeElement).toBe(closeBtn());
+    } finally {
+      removeLayer(hover);
+    }
+  });
+
   it("Tab reaches a toast shown inside the dialog, and wraps from it", () => {
     // The dialog's toast host sits beside the panel; trapped to the panel, a toast's Undo or dismiss
     // could not be reached from the keyboard at all.