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/AlbumModal.tsx

@@ -1,5 +1,7 @@
 /** The album detail sheet: cover, metadata, and a numbered track list. */
 
+import { useEffect, useRef } from "react";
+
 import type { Album } from "../api/types";
 import { isBook, unitLabel } from "../lib/covers";
 import { clock } from "../lib/format";
@@ -9,6 +11,8 @@ interface Props {
   album: Album;
   currentAlbumId: string | null;
   currentTrackIndex: number;
+  /** The track Ctrl+j/k has highlighted, so the keyboard has something visible to move. */
+  selectedIndex: number;
   onClose: () => void;
   onPlay: (trackIndex: number) => void;
 }
@@ -17,13 +21,32 @@ export function AlbumModal({
   album,
   currentAlbumId,
   currentTrackIndex,
+  selectedIndex,
   onClose,
   onPlay,
 }: Props) {
   const book = isBook(album);
+  const sheet = useRef<HTMLDivElement | null>(null);
+
+  // Keep the Ctrl+j/k highlight on screen as it moves past the fold, the same way the
+  // browse grid keeps its own keyboard selection visible.
+  useEffect(() => {
+    const box = sheet.current;
+    const element = box?.querySelector<HTMLElement>(`[data-nav-index="${selectedIndex}"]`);
+    if (!box || !element) return;
+    const top = element.offsetTop - box.offsetTop;
+    const bottom = top + element.offsetHeight;
+    const pad = 12;
+    if (top - pad < box.scrollTop) box.scrollTop = Math.max(0, top - pad);
+    else if (bottom + pad > box.scrollTop + box.clientHeight) {
+      box.scrollTop = bottom + pad - box.clientHeight;
+    }
+  }, [selectedIndex]);
+
   return (
     <div className="overlay" style={{ zIndex: 4, background: "oklch(15% 0.03 210 / .6)" }} onClick={onClose}>
       <div
+        ref={sheet}
         onClick={(event) => event.stopPropagation()}
         style={{
           background: "oklch(96% 0.012 210)",
@@ -128,6 +151,7 @@ export function AlbumModal({
             return (
               <button
                 key={index}
+                data-nav-index={index}
                 onClick={() => onPlay(index)}
                 style={{
                   display: "flex",
@@ -142,6 +166,8 @@ export function AlbumModal({
                   background: current
                     ? "oklch(70% 0.16 340 / .16)"
                     : "oklch(30% 0.03 210 / .05)",
+                  outline: index === selectedIndex ? "3px solid var(--accent)" : "none",
+                  outlineOffset: 2,
                 }}
               >
                 <div

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"],
 ];