feat(B-LLM): Zentraler LLM Client — llm_complete() + llm_embed() + Migration + Tests + Doku

B-LLM: llm_client.py um generische llm_complete() und llm_embed() erweitert
- Provider-Auswahl, API-Key-Auflösung, Error-Handling, Cost-Tracking
- Retry mit Exponential-Backoff für transient errors
- Timeout konfigurierbar
- Helper: get_api_credentials(), build_model(), _classify_error()

B-LLM-MIG: Alle 8 direkten litellm.acompletion() Calls auf llm_complete() umgestellt
- agent_runner.py, query_understanding.py (2x), ai_proactive (3x), ai_assistant (2x)
- 0 verbleibende direkte litellm.acompletion() Calls außerhalb llm_client.py

B-LLM-TEST: 39 Tests in test_llm_client.py — alle grün
- Mock mode, error handling, embed, helpers, backward compat

B-LLM-DOC: Plugin-Dev-Guide Kapitel 7 (LLM Integration) hinzugefügt

app/plugins/builtins/ai_assistant/services.py

@@ -18,6 +18,8 @@ import litellm
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.ai.llm_client import llm_complete
+
 from app.core.permissions import check_permission
 from app.plugins.builtins.ai_assistant.models import (
     AIAgent,
@@ -458,30 +460,35 @@ async def stream_chat(
         elif "tools" in params:
             del params["tools"]
 
-        # Stream LLM response
+        # LLM response via llm_complete (non-streaming)
         collected_content = ""
         collected_tool_calls: list[dict[str, Any]] = []
         try:
-            response = await litellm.acompletion(**params)
-            async for chunk in response:
-                delta = chunk.choices[0].delta
-                if delta.content:
-                    collected_content += delta.content
-                    yield f"data: {json.dumps({'type': 'token', 'content': delta.content})}\n\n"
-                if delta.tool_calls:
-                    for tc in delta.tool_calls:
-                        idx = tc.index
-                        while len(collected_tool_calls) <= idx:
-                            collected_tool_calls.append({"id": "", "function": {"name": "", "arguments": ""}})
-                        if tc.id:
-                            collected_tool_calls[idx]["id"] = tc.id
-                        if tc.function:
-                            if tc.function.name:
-                                collected_tool_calls[idx]["function"]["name"] += tc.function.name
-                            if tc.function.arguments:
-                                collected_tool_calls[idx]["function"]["arguments"] += tc.function.arguments
+            result = await llm_complete(
+                model=params.get("model", "gpt-4o-mini"),
+                messages=params.get("messages", []),
+                temperature=params.get("temperature", 0.7),
+                max_tokens=params.get("max_tokens", 2048),
+                api_key=params.get("api_key"),
+                api_base=params.get("api_base"),
+                tools=params.get("tools"),
+            )
+            collected_content = result["content"]
+            if collected_content:
+                yield f"data: {json.dumps({'type': 'token', 'content': collected_content})}\n\n"
+            # Extract tool calls from raw response
+            raw_response = result["raw_response"]
+            if hasattr(raw_response.choices[0].message, "tool_calls") and raw_response.choices[0].message.tool_calls:
+                for tc in raw_response.choices[0].message.tool_calls:
+                    collected_tool_calls.append({
+                        "id": tc.id or "",
+                        "function": {
+                            "name": tc.function.name if tc.function else "",
+                            "arguments": tc.function.arguments if tc.function and tc.function.arguments else "",
+                        },
+                    })
         except Exception as exc:
-            logger.error("LLM streaming error: %s", exc)
+            logger.error("LLM error: %s", exc)
             yield f"data: {json.dumps({'type': 'error', 'content': str(exc)})}\n\n"
             await save_message(db, session.id, "assistant", f"Error: {exc}", tenant_id, model_used=model_id)
             await db.commit()