Add a vim-style keyboard layer: Ctrl navigates, Shift controls transport

Ctrl+h/j/k/l move the highlight in whatever list is on screen - the browse
grid, search results, or an open album's track list - the same job the
arrow keys already do, just reachable without leaving the home row.
Ctrl+d/u add vim's own half-page jump. Shift+h/j/k/l/m are transport
(previous/next, volume, mute) from anywhere, including the room page,
matching the muscle memory of other vim-ish media apps; every other
Shift+letter still reaches search untouched; only the shifted letter
form of those five keys is intercepted.

Shift+Enter opens an album's track list (the keyboard equivalent of
clicking its cover, which had no key of its own until now) instead of
playing it outright; Ctrl+j/k then move a visible highlight through that
list, and Enter plays whichever track is highlighted. Falls back to plain
ENTER's behaviour for a category tile or a podcast episode, neither of
which has a track list to show.

Mute (Shift+M) is new - nothing was bound to it before.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/components/HelpOverlay.tsx

@@ -3,16 +3,20 @@
 
 const KEYS: Array<[caps: string[], label: string]> = [
   [["LEER"], "Play / Pause"],
-  [["CTRL+H", "CTRL+L"], "Song zurück / vor"],
-  [["CTRL+J", "CTRL+K"], "Leiser / lauter"],
+  [["SHIFT+H", "SHIFT+L"], "Song zurück / vor"],
+  [["SHIFT+J", "SHIFT+K"], "Leiser / lauter"],
+  [["SHIFT+M"], "Stumm"],
   [["⇧←", "⇧→"], "15 Sekunden zurück / vor"],
+  [["← ↑ ↓ →"], "Auswahl bewegen"],
+  [["CTRL+H/J/K/L"], "Auswahl bewegen (Raster oder Titelliste)"],
+  [["CTRL+D", "CTRL+U"], "Eine halbe Seite weiter / zurück"],
   [["A-Z"], "Album oder Hörbuch suchen"],
   [["?"], "Einzelne Titel suchen"],
-  [["F1"], "Diese Hilfe"],
   [["TAB"], "Musik / Hörbücher / Podcasts"],
-  [["A", "0-9"], "Aktuellen Titel einer Fernbedienungs-Taste zuweisen"],
-  [["← ↑ ↓ →"], "Auswahl bewegen"],
   [["ENTER"], "Auswahl abspielen"],
+  [["⇧ENTER"], "Titelliste öffnen"],
+  [["A", "0-9"], "Aktuellen Titel einer Fernbedienungs-Taste zuweisen"],
+  [["F1"], "Diese Hilfe"],
   [["ESC"], "Schließen / Suche löschen"],
 ];