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/i18n/locales/en/keys.json

@@ -18,7 +18,7 @@
   "home": "Go to Home (what should I watch?)",
   "info": "Media info",
   "stats": "Stats for nerds",
-  "back": "Stop & back to feed",
+  "back": "Stop & go back",
   "browseBack": "Back one level",
   "closePlayer": "Close the player",
   "palette": "Open the jump-to palette",
@@ -34,5 +34,9 @@
   "search": "Jump to the search box",
   "listStep": "Next / previous item",
   "gridMove": "Move around the list",
-  "open": "Open the selected item"
+  "open": "Open the selected item",
+  "cap": {
+    "space": "Space",
+    "menu": "Menu"
+  }
 }

frontend/src/i18n/locales/hu/keys.json

@@ -18,7 +18,7 @@
   "home": "Ugrás a kezdőlapra (mit nézzek?)",
   "info": "Média infó",
   "stats": "Statisztika (nerdöknek)",
-  "back": "Leállítás és vissza a feedre",
+  "back": "Leállítás és vissza",
   "browseBack": "Vissza egy szintet",
   "closePlayer": "Lejátszó bezárása",
   "palette": "Ugrás-paletta megnyitása",
@@ -34,5 +34,9 @@
   "search": "Ugrás a keresőbe",
   "listStep": "Következő / előző elem",
   "gridMove": "Mozgás a listában",
-  "open": "A kijelölt elem megnyitása"
+  "open": "A kijelölt elem megnyitása",
+  "cap": {
+    "space": "Szóköz",
+    "menu": "Menü"
+  }
 }