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/src/core/config.py

@@ -157,6 +157,28 @@ class Settings(BaseSettings):
         description="Trace sampling rate (1.0 = 100%)",
     )
 
+    # ==========================================================================
+    # Langfuse LLMOps (Phase 15.1)
+    # LLM 呼叫追蹤、成本監控、Prompt 版本管理
+    # 端點: http://192.168.0.110:3100 (DevOps 金庫)
+    # ==========================================================================
+    LANGFUSE_ENABLED: bool = Field(
+        default=True,
+        description="Enable Langfuse LLM observability",
+    )
+    LANGFUSE_URL: str = Field(
+        default="http://192.168.0.110:3100",
+        description="Langfuse self-hosted URL",
+    )
+    LANGFUSE_PUBLIC_KEY: str = Field(
+        default="",
+        description="Langfuse public key (from K8s Secret)",
+    )
+    LANGFUSE_SECRET_KEY: str = Field(
+        default="",
+        description="Langfuse secret key (from K8s Secret)",
+    )
+
     # ==========================================================================
     # AI Fallback Strategy (ADR-006)
     # Order: Ollama (local) -> Gemini (cloud) -> Claude (cloud)
@@ -224,8 +246,8 @@ class Settings(BaseSettings):
         description="OpenClaw AI Agent service URL",
     )
     OPENCLAW_DEFAULT_MODEL: str = Field(
-        default="llama3.2:3b",
-        description="Default Ollama model for RCA analysis",
+        default="qwen2.5:7b-instruct",
+        description="Default Ollama model for RCA analysis (7B params, better Chinese)",
     )
     OPENCLAW_TIMEOUT: int = Field(
         default=90,