feat: Konversationsgedaechtnis - Kurzzeit-Gespraechsverlauf pro Session

- Store: messages-Tabelle + append_message/get_recent_messages (mit Mandanten-Schutz)
- LLMProvider.complete um history erweitert (openrouter + local bauen system+history+user)
- Orchestrator.chat_text reicht den Verlauf ans LLM weiter
- chat.py: bei session_id letzte HISTORY_MAX_MESSAGES laden, danach User-/Assistant-Turn speichern
- ohne session_id weiterhin zustandslos; ?debug zeigt history_len
- Config HISTORY_MAX_MESSAGES (Default 10)
- Tests: 32 gruen (3 neue Gedaechtnis-Tests)
- Doku aktualisiert (README, BEDIENUNGSANLEITUNG, Architektur)

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

tests/test_memory.py

@@ -0,0 +1,65 @@
+from fastapi.testclient import TestClient
+
+import app.dependencies as deps
+from app.main import app
+
+client = TestClient(app)
+
+
+def _install_stubs(monkeypatch, captured):
+    class MemLLM:
+        async def complete(self, text, history=None, session_id=None):
+            captured["history"] = list(history or [])
+            return f"Antwort auf: {text}"
+
+    class StubTTS:
+        async def synthesize(self, text, voice=None, audio_format="pcm"):
+            return b"AUDIO"
+
+    monkeypatch.setitem(deps.LLM_REGISTRY, "mem", lambda s: MemLLM())
+    monkeypatch.setitem(deps.TTS_REGISTRY, "stub", lambda s: StubTTS())
+    return {"llm_provider": "mem", "tts_provider": "stub", "output_endpoint": "loopback"}
+
+
+def test_history_accumulates_and_flows_to_llm(monkeypatch):
+    captured = {}
+    base = _install_stubs(monkeypatch, captured)
+
+    # Turn 1: noch kein Verlauf.
+    r1 = client.post("/api/chat?debug=true&session_id=conv1", json={"text": "Hallo", **base})
+    assert r1.status_code == 200
+    assert r1.json()["history_len"] == 0
+    assert captured["history"] == []
+
+    # Turn 2: Verlauf enthaelt User+Assistant aus Turn 1.
+    r2 = client.post("/api/chat?debug=true&session_id=conv1", json={"text": "Und weiter?", **base})
+    assert r2.status_code == 200
+    assert r2.json()["history_len"] == 2
+    assert captured["history"] == [
+        {"role": "user", "content": "Hallo"},
+        {"role": "assistant", "content": "Antwort auf: Hallo"},
+    ]
+
+
+def test_no_session_id_is_stateless(monkeypatch):
+    captured = {}
+    base = _install_stubs(monkeypatch, captured)
+
+    client.post("/api/chat?debug=true", json={"text": "A", **base})
+    client.post("/api/chat?debug=true", json={"text": "B", **base})
+    assert captured["history"] == []  # ohne session_id kein Gedaechtnis
+
+
+def test_history_limited_by_setting(monkeypatch):
+    from app.config import settings
+
+    captured = {}
+    base = _install_stubs(monkeypatch, captured)
+    monkeypatch.setattr(settings, "history_max_messages", 2)
+
+    for text in ("eins", "zwei", "drei"):
+        client.post("/api/chat?debug=true&session_id=limit", json={"text": text, **base})
+
+    # Vor dem 3. Turn liegen 4 Nachrichten vor; geladen werden nur die letzten 2.
+    assert len(captured["history"]) == 2
+    assert captured["history"][-1] == {"role": "assistant", "content": "Antwort auf: zwei"}