fix(api): 補齊 prometheus-client 依賴 + 停用 Nightly LLM Tests

首席架構師審查 2026-03-29:
- 問題: metrics.py import prometheus_client 但未加入依賴
- 影響: API Pod CrashLoopBackOff
- 修復: 新增 prometheus-client>=0.20.0

統帥指示: 停用 Nightly LLM Tests 減少 Runner 負載

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

apps/api/pyproject.toml

@@ -28,6 +28,8 @@ dependencies = [
     "sentry-sdk[fastapi]>=2.0.0",
     # Langfuse (LLMOps - Phase 15.1，Self-Hosted @ 192.168.0.110:3100)
     "langfuse>=2.0.0",
+    # Prometheus (ADR-037 Wave A.5 監控指標)
+    "prometheus-client>=0.20.0",
     # Phase 6.4g: leWOOOgo Brain - 積木化決策引擎
     # NOTE: Local packages 透過 Dockerfile 預先安裝，無需在此列出
     # 請參閱 apps/api/Dockerfile Phase 6.4i 註解