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/lib/keymap.ts

@@ -297,7 +297,14 @@ function liveSequence(e: KeyboardEvent): typeof pending {
     pending = null;
     return null;
   }
-  return MODIFIER_KEYS.has(e.key) ? null : pending;
+  if (MODIFIER_KEYS.has(e.key)) return null;
+  // A chord with a modifier cannot be a second step (no binding may need one, D1): it abandons the
+  // sequence and is matched as itself, or `g` then Mod+K would open the browser's search, not ours.
+  if (e.ctrlKey || e.metaKey || e.altKey || e.shiftKey) {
+    pending = null;
+    return null;
+  }
+  return pending;
 }
 
 const stepsOf = (chord: string): string[] => chord.split(" ");