feat(workspace): dictation via /diktat (M4)

/diktat (only in an empty bullet, only with voice input available)
listens right away; the bullet becomes one button with the live wave
across it and a translucent "Stopp" on top. A tap ends it and the
recognised text lands in the bullet as plain text. Uses the configured
speech recognition (own Whisper server or the browser); Esc cancels.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/workspace/DictationBlock.tsx

@@ -0,0 +1,97 @@
+import React, { useEffect, useRef, useState } from 'react';
+import { Loader2, Square } from 'lucide-react';
+import { useVoiceInput } from '../../lib/useVoiceInput';
+import { VoiceWave } from '../../components/VoiceWave';
+import { triggerHaptic } from '../../lib/api';
+
+interface DictationBlockProps {
+  onDone: (text: string) => void;
+  onCancel: () => void;
+}
+
+// What an empty bullet turns into after /diktat: listening starts right away, the whole bullet is one
+// button with the live wave and a translucent "Stopp" on top. A tap ends it; the text lands in the
+// bullet as plain text.
+export const DictationBlock: React.FC<DictationBlockProps> = ({ onDone, onCancel }) => {
+  const [interim, setInterim] = useState('');
+  const [error, setError] = useState<string | null>(null);
+  const doneRef = useRef(false);
+  const buttonRef = useRef<HTMLButtonElement>(null);
+
+  const voice = useVoiceInput({
+    continuous: true,
+    onText: (text, final) => {
+      if (!final) {
+        setInterim(text);
+        return;
+      }
+      if (doneRef.current) return;
+      doneRef.current = true;
+      if (text.trim()) onDone(text.trim());
+      else onCancel();
+    },
+    onError: (message) => {
+      setError(message);
+      window.setTimeout(() => {
+        if (!doneRef.current) {
+          doneRef.current = true;
+          onCancel();
+        }
+      }, 2500);
+    },
+  });
+
+  useEffect(() => {
+    triggerHaptic([15, 60, 25]);
+    void voice.start();
+    buttonRef.current?.focus();
+    // start once when the bullet turns into the dictation
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
+  const transcribing = voice.state === 'transcribing';
+
+  return (
+    <button
+      ref={buttonRef}
+      type="button"
+      onClick={() => {
+        if (voice.state === 'listening') {
+          triggerHaptic(20);
+          void voice.stop();
+        }
+      }}
+      onKeyDown={(e) => {
+        if (e.key === 'Escape') {
+          e.preventDefault();
+          doneRef.current = true;
+          voice.cancel();
+          onCancel();
+        }
+      }}
+      disabled={transcribing || !!error}
+      aria-label="Diktat beenden"
+      className="relative w-full min-h-[56px] sm:min-h-[44px] my-1 rounded-card border border-accent bg-accent-dim overflow-hidden flex items-center justify-center cursor-pointer disabled:cursor-default focus:outline-none"
+    >
+      {/* Live wave across the whole bullet */}
+      <VoiceWave getLevel={voice.level} bars={32} className="absolute inset-x-3 inset-y-2 justify-between h-auto text-accent opacity-60" />
+      {interim && !error && (
+        <span className="absolute inset-x-3 bottom-1 text-[11px] text-main truncate text-left pointer-events-none">{interim}</span>
+      )}
+      {/* Floating stop label on top */}
+      <span className="relative z-10 flex items-center gap-1.5 px-3 py-1 rounded-pill bg-panel/70 text-main text-xs font-semibold backdrop-blur-sm">
+        {error ? (
+          <span className="text-status-err font-normal">{error}</span>
+        ) : transcribing ? (
+          <>
+            <Loader2 className="w-3.5 h-3.5 animate-spin" /> Wird erkannt…
+          </>
+        ) : (
+          <>
+            <Square className="w-3 h-3 fill-current" /> Stopp
+          </>
+        )}
+      </span>
+    </button>
+  );
+};