Streaming assistant message

<pk-message class="justify-end">
  <pk-message-content
    class="bg-primary text-primary-foreground"
    content="Show me a small computed() example."
  />
</pk-message>

<pk-message>
  <pk-message-avatar src="" alt="Assistant" fallback="AI" />
  <pk-response-stream
    class="prose prose-sm dark:prose-invert max-w-none"
    [textStream]="streamed()"
    [markdown]="true"
    [speed]="80"
  />
</pk-message>

<pk-stream-controls
  [state]="state()"
  (stop)="stop()"
  (regenerate)="start()"
/>

// Component — chunked append while streaming.
// pk-markdown re-renders on each update; partial markdown still renders gracefully.
protected readonly state = signal<StreamControlsState>('idle');
protected readonly streamed = signal('');

protected start(): void {
  this.streamed.set('');
  this.state.set('streaming');
  const chunks = FULL_RESPONSE.match(/.{1,40}/gs) ?? [];
  let i = 0;
  const tick = () => {
    if (this.state() !== 'streaming') return;
    if (i >= chunks.length) { this.state.set('idle'); return; }
    this.streamed.update(v => v + chunks[i++]);
    setTimeout(tick, 120);
  };
  setTimeout(tick, 120);
}

protected stop(): void { this.state.set('idle'); }