feat(keys): the conversation list walks with j/k; the cheat sheet names keys in the reader's language

E11 S5 — the HU/EN sweep and the keyboard-only pass over every module.

- The keyboard cheat sheet printed "Space" and "Menu" on a Hungarian sheet: a keycap that carries a
  WORD (not a legend every layout prints alike, like Esc, Ctrl or Enter) is now named by the caller in
  the reader's language (`formatChord(chord, words)`, `keys.cap.*`: Szóköz / Menü).
- The Plex player's ⌫/Esc line said "Stop & back to feed", but the player goes back to wherever it
  was opened from (Home, a Plex page): "Stop & go back" / "Leállítás és vissza".
- Messages: the conversation list is a keyboard list (NavGrid + navItemAttrs, the name button is the
  open element; the pop-out button keeps its own Enter). D1 covers every list whose rows open one
  thing; this one was missed in S4. Notification cards have no single open action and stay out, like
  the download queue.

Sweep, measured: every static `t("…")` key used in the source exists in both languages (the only
misses are template prefixes); the HU values equal to EN are proper nouns and loanwords (Admin, Plex,
Trakt, Shorts). Palette in Hungarian: "téma" makes "Téma: Midnight" the active row ahead of the channel
"Topik - mindig témában", live region "7 találat".

Keyboard-only pass in Chrome, Hungarian UI — 1024×768: every `g` chord lands on its module, `j` rings
the first item (solid 2px accent) on Home, Feed, Channels, Playlists, Plex and Downloads, `s` focuses
the search on Feed, Channels, Playlists and Plex, no page scrolls sideways. 3440×1440: `j` → → ↓
walks Home, Feed (8 columns: 0 → 1 → 9), Channels, Playlists, Plex and Downloads, no sideways scroll.
The help sheet lists every line translated; inside the Plex player "Szóköz / K" and "⌫ / Esc
Leállítás és vissza". Messages: a real `j` rings the row, Enter opens the thread.

frontend/src/components/ui/KeyboardHelp.tsx

@@ -47,6 +47,7 @@ export default function KeyboardHelp() {
     ? scopes.filter((s) => !isPageLevelScope(s) && s !== "contextMenu")
     : scopes;
   const lines = helpLines(live, pages).filter((l) => !l.when || !!conditions[l.when]);
+  const words = { Space: t("keys.cap.space"), ContextMenu: t("keys.cap.menu") };
   return (
     <Modal title={t("keys.title")} onClose={closeKeyboardHelp} maxWidth="max-w-md">
       <dl className="grid grid-cols-[auto_1fr] items-center gap-x-4 gap-y-2.5 text-sm">
@@ -58,7 +59,7 @@ export default function KeyboardHelp() {
                   key={chord}
                   className="rounded-sm border border-border bg-surface px-1.5 py-0.5 text-xs font-mono whitespace-nowrap"
                 >
-                  {formatChord(chord)}
+                  {formatChord(chord, words)}
                 </kbd>
               ))}
             </dt>