feat(gpu-server): add API key auth, VRAM management, and Piper TTS voices

- Add API key authentication to all GPU services (X-API-Key header)
  - /health and /docs remain public (no key needed)
  - Shared key configured via GPU_API_KEY env variable
- Add VRAM auto-unload for mana-image-gen (5min) and mana-stt (10min)
  - FLUX.2 pipeline freed after idle, recovering ~13GB VRAM
  - WhisperX models freed after idle, recovering ~3GB VRAM
- Install Piper TTS voices (Thorsten + Kerstin) for local German TTS
- Update @manacore/shared-gpu client to support apiKey parameter
- Add GPU_API_KEY to .env.development
- Document API auth and VRAM management in setup guide

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-gpu/src/gpu-client.ts

@@ -28,8 +28,10 @@ export class GpuClient {
 	public readonly stt: SttClient;
 	public readonly tts: TtsClient;
 	public readonly image: ImageClient;
+	public readonly apiKey?: string;
 
 	constructor(config: GpuServiceConfig) {
+		this.apiKey = config.apiKey;
 		this.stt = new SttClient(config);
 		this.tts = new TtsClient(config);
 		this.image = new ImageClient(config);