refactor(ai): 模組化重構 - NVIDIA chat 移至 NvidiaProvider

符合 feedback_lewooogo_modular_enforcement.md 規範:
- 移除 openclaw.py 中的 _call_nvidia() (重複邏輯)
- 新增 NvidiaProvider.chat() 方法
- 更新 INvidiaProvider Protocol
- openclaw.py 改用 get_nvidia_provider().chat()
- 測試移至 test_nvidia_chat.py

架構層次:
- Router → Service → Provider (正確)
- 禁止 Service 層重複實作已存在的 Provider 功能

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

apps/api/src/services/openclaw.py

@@ -461,76 +461,8 @@ class OpenClawService:
             logger.warning("claude_call_failed", error=str(e))
             return str(e), False
 
-    async def _call_nvidia(self, prompt: str) -> tuple[str, bool, int, float]:
-        """
-        呼叫 NVIDIA Nemotron (OpenAI 相容格式)
-
-        2026-03-29 ogt: 新增 Nemotron 一般告警支援 (非 Tool Calling)
-        2026-03-29 ogt: P1 修復 - 從 ModelRegistry 取得模型名稱
-
-        Returns:
-            tuple: (response_text, success, total_tokens, cost_usd)
-        """
-        if not settings.NVIDIA_API_KEY:
-            return "NVIDIA_API_KEY not configured", False, 0, 0.0
-
-        try:
-            client = await self._get_client()
-
-            # 從 ModelRegistry 取得模型 (P1-1 修復)
-            registry = get_model_registry()
-            model_name = registry.get_model("nvidia", "rca")
-            options = registry.get_provider_options("nvidia")
-
-            logger.info(
-                "nvidia_request_start",
-                model=model_name,
-                prompt_length=len(prompt),
-            )
-
-            response = await client.post(
-                "https://integrate.api.nvidia.com/v1/chat/completions",
-                headers={
-                    "Authorization": f"Bearer {settings.NVIDIA_API_KEY}",
-                    "Content-Type": "application/json",
-                },
-                json={
-                    "model": model_name,
-                    "messages": [{"role": "user", "content": prompt}],
-                    "temperature": options.get("temperature", 0.1),
-                    "max_tokens": options.get("max_tokens", 2048),
-                    "response_format": {"type": "json_object"},  # 強制 JSON
-                },
-                timeout=60.0,
-            )
-            response.raise_for_status()
-            data = response.json()
-
-            text = data["choices"][0]["message"]["content"]
-
-            # Token 用量
-            usage = data.get("usage", {})
-            prompt_tokens = usage.get("prompt_tokens", 0)
-            completion_tokens = usage.get("completion_tokens", 0)
-            total_tokens = usage.get("total_tokens", prompt_tokens + completion_tokens)
-
-            # NVIDIA NIM 免費 tier = $0
-            cost_usd = 0.0
-
-            logger.info(
-                "nvidia_response_received",
-                model=model_name,
-                response_length=len(text),
-                prompt_tokens=prompt_tokens,
-                completion_tokens=completion_tokens,
-                total_tokens=total_tokens,
-                cost_usd=f"${cost_usd:.6f}",
-            )
-            return text, True, total_tokens, cost_usd
-
-        except Exception as e:
-            logger.warning("nvidia_call_failed", error=str(e), error_type=type(e).__name__)
-            return str(e), False, 0, 0.0
+    # 2026-03-29 ogt: _call_nvidia 已移至 nvidia_provider.py
+    # 符合模組化規範 - 所有 NVIDIA API 呼叫統一由 NvidiaProvider 處理
 
     # =========================================================================
     # Mock LLM - Intelligent Fallback with SignOz Data
@@ -948,8 +880,10 @@ class OpenClawService:
                 elif provider == "gemini":
                     response, success, total_tokens, cost_usd = await self._call_gemini(prompt)
                 elif provider == "nvidia":
-                    # 2026-03-29 ogt: Nemotron 一般告警支援
-                    response, success, total_tokens, cost_usd = await self._call_nvidia(prompt)
+                    # 2026-03-29 ogt: 使用 NvidiaProvider.chat() (模組化規範)
+                    from src.services.nvidia_provider import get_nvidia_provider
+                    nvidia_provider = get_nvidia_provider()
+                    response, success, total_tokens, cost_usd = await nvidia_provider.chat(prompt)
                 elif provider == "claude":
                     response, success = await self._call_claude(prompt)
                 else: