feat(api): Phase 15.1 Langfuse LLMOps 整合 + 模型升級

## 新功能
- Langfuse 自建部署 (192.168.0.110:3100)
- langfuse_client.py - LLM 呼叫追蹤包裝
- OpenClaw 整合 Langfuse trace

## 模型升級 (統帥批准)
- 生產預設: llama3.2:3b → qwen2.5:7b-instruct
- 摘要任務: llama3.2:3b (速度優先)

## 配置更新
- requirements.txt: +langfuse>=2.0.0
- config.py: +LANGFUSE_* 設定
- models.json: 更新 Ollama 模型配置
- K8s: Secret + ConfigMap 更新

## 審查通過
- 模組化檢查 ✅
- 核心測試 31/31 ✅

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/models.json

@@ -3,7 +3,7 @@
   "name": "OpenClaw AI Router Configuration",
   "version": "1.0.0",
   "description": "AI 模型路由與備援設定 (ADR-006)",
-  "updated_at": "2026-03-21",
+  "updated_at": "2026-03-26",
 
   "default_provider": "ollama",
   "fallback_order": ["ollama", "gemini", "claude"],
@@ -16,9 +16,9 @@
       "endpoint": "http://192.168.0.188:11434",
       "api_path": "/api/generate",
       "models": {
-        "default": "llama3.2:3b",
-        "rca": "llama3.2:3b",
-        "summary": "llama3.2:1b"
+        "default": "qwen2.5:7b-instruct",
+        "rca": "qwen2.5:7b-instruct",
+        "summary": "llama3.2:3b"
       },
       "options": {
         "temperature": 0.1,