feat(cicd): #46c OTEL Tracing 遷移到 Gitea workflows

- CD: awoooi-cd service (192.168.0.188:24318)
- E2E: awoooi-e2e service
- 環境變數: OTEL_EXPORTER_OTLP_ENDPOINT, OTEL_SERVICE_NAME, OTEL_RESOURCE_ATTRIBUTES

原 GitHub workflows (cd7d63e) → Gitea workflows (ADR-039)

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

apps/api/src/main.py

@@ -26,7 +26,8 @@ import sentry_sdk
 import structlog
 from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse
+from fastapi.responses import JSONResponse, Response
+from prometheus_client import CONTENT_TYPE_LATEST, generate_latest
 from sentry_sdk.integrations.fastapi import FastApiIntegration
 from sentry_sdk.integrations.starlette import StarletteIntegration
 
@@ -437,6 +438,21 @@ app.include_router(
 )
 
 
+# =============================================================================
+# Prometheus Metrics Endpoint
+# =============================================================================
+# 2026-03-31 ogt: 暴露 Prometheus 指標供告警系統使用
+
+
+@app.get("/metrics", include_in_schema=False)
+async def prometheus_metrics() -> Response:
+    """Prometheus metrics endpoint for alerting"""
+    return Response(
+        content=generate_latest(),
+        media_type=CONTENT_TYPE_LATEST,
+    )
+
+
 # =============================================================================
 # Root Endpoint
 # =============================================================================