feat(ai): ADR-036 NVIDIA Nemotron Tool Calling 整合

Phase 20 - 提升 Tool Calling 精準度 50% → 83.3%

新增:
- src/models/nvidia.py: Pydantic Schema
- src/services/nvidia_provider.py: NvidiaProvider 類別
- tests/test_nvidia_provider.py: 15 項單元測試 (全部通過)

修改:
- ai_router.py: AIProvider.NVIDIA + route_tool_calling()
- ai_rate_limiter.py: NVIDIA 限制 (5 RPM, 100/day)
- models.json: NVIDIA 配置
- cd.yaml: Secrets 注入 NVIDIA_API_KEY

路由策略:
- Tool Calling: Nemotron → Gemini → Claude
- 一般對話: Ollama → Gemini → Claude (不變)

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

apps/api/src/core/config.py

@@ -201,8 +201,9 @@ class Settings(BaseSettings):
     )
 
     # ==========================================================================
-    # AI Fallback Strategy (ADR-006)
+    # AI Fallback Strategy (ADR-006 v1.3 + ADR-036)
     # Order: Ollama (local) -> Gemini (cloud) -> Claude (cloud)
+    # Tool Calling: Nemotron (專用) -> Gemini -> Claude
     # ==========================================================================
     AI_FALLBACK_ORDER: list[str] = Field(
         default=["ollama", "gemini", "claude"],
@@ -210,6 +211,11 @@ class Settings(BaseSettings):
     )
     GEMINI_API_KEY: str = Field(default="", description="Google Gemini API key")
     CLAUDE_API_KEY: str = Field(default="", description="Anthropic Claude API key")
+    # 2026-03-29 ogt: ADR-036 Nemotron Tool Calling 整合
+    NVIDIA_API_KEY: str = Field(
+        default="",
+        description="NVIDIA NIM API key for Nemotron Tool Calling (ADR-036)",
+    )
 
     @field_validator("AI_FALLBACK_ORDER", mode="before")
     @classmethod