feat: Token-Level-LLM-Streaming über WebSocket (#4 Ausbau)

- LLMProvider.stream: Basis-Default (Fallback über complete) + SSE-Streaming
  fuer OpenRouter und lokalen OpenAI-kompatiblen Provider; gemeinsamer Parser sse_delta
- Orchestrator.chat_stream: LLM-Token live via on_token-Callback, danach
  Spoken-Adapter/Normalizer/TTS/Output; Fallback fuer Provider ohne stream
- WS /ws/chat: opt-in {"stream":true} -> ack -> token* -> semantic -> audio -> done
- Tests: 43 gruen (+5: SSE-Parsing, Default-Fallback, WS-Token-Flow)
- Doku aktualisiert; .gitignore: *.wav (generierte Audio-Ausgaben)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/api/ws.py

@@ -95,14 +95,28 @@ async def ws_chat(
             await websocket.send_json({"type": "ack", "route": route.as_dict()})
 
             voice = msg.get("voice") or settings.openrouter_tts_voice
+            stream = bool(msg.get("stream"))
             try:
-                trace, audio = await orchestrator.chat_text(
-                    text,
-                    language=route.language,
-                    voice=voice,
-                    output=output,
-                    history=llm_context,
-                )
+                if stream:
+                    async def on_token(delta):
+                        await websocket.send_json({"type": "token", "text": delta})
+
+                    trace, audio = await orchestrator.chat_stream(
+                        text,
+                        language=route.language,
+                        voice=voice,
+                        output=output,
+                        history=llm_context,
+                        on_token=on_token,
+                    )
+                else:
+                    trace, audio = await orchestrator.chat_text(
+                        text,
+                        language=route.language,
+                        voice=voice,
+                        output=output,
+                        history=llm_context,
+                    )
             except Exception as exc:
                 await websocket.send_json({"type": "error", "status": 502, "detail": str(exc)})
                 continue