feat(api): Phase 15.3 Deep Linking 三系統互連

實現 Sentry ↔ SignOz ↔ Langfuse 零斷鏈觀測:

新增 deep_linking.py:
- SignOz Trace URL 生成器
- Langfuse Trace URL 生成器
- Sentry Issue URL 生成器
- get_all_links() 統一取得所有連結

整合點:
- main.py: Sentry before_send 注入 otel_trace_id + signoz_trace_url
- langfuse_client.py: 自動注入 OTEL trace_id 到 metadata
- openclaw.py: SignOz span 記錄 langfuse.trace_id 反向連結

架構圖:
┌─────────┐ trace_id ┌─────────┐ trace_id ┌──────────┐
│ Sentry  │◄────────►│ SignOz  │◄────────►│ Langfuse │
│ Errors  │          │ Traces  │          │ LLMOps   │
└─────────┘          └─────────┘          └──────────┘

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

apps/api/src/services/openclaw.py

@@ -832,7 +832,7 @@ class OpenClawService:
             logger.info("mock_mode_enabled", using="mock_llm")
             return self._generate_mock_response(alert_context or {}, signoz_metrics), "mock", True
 
-        # Phase 15.1: Langfuse 追蹤整合
+        # Phase 15.1 + 15.3: Langfuse 追蹤整合 + SignOz Deep Linking
         with langfuse_trace(
             "openclaw_fallback_chain",
             metadata={
@@ -841,6 +841,21 @@ class OpenClawService:
                 "alert_fingerprint": (alert_context or {}).get("fingerprint", "unknown"),
             },
         ) as trace:
+            # Phase 15.3: SignOz → Langfuse 反向連結
+            # 在當前 OTEL span 中記錄 Langfuse trace_id
+            if trace.langfuse_trace_id:
+                from opentelemetry import trace as otel_trace
+
+                from src.core.deep_linking import DeepLinking
+
+                current_span = otel_trace.get_current_span()
+                if current_span:
+                    current_span.set_attribute("langfuse.trace_id", trace.langfuse_trace_id)
+                    current_span.set_attribute(
+                        "langfuse.trace_url",
+                        DeepLinking.langfuse_trace_url(trace.langfuse_trace_id),
+                    )
+
             for provider in settings.AI_FALLBACK_ORDER:
                 logger.info("ai_provider_attempt", provider=provider)