feat(batch-agent): integrate Langfuse tracing

- tracing.py: init/shutdown, trace_span, get_langfuse_callback, prompt mgmt
- main.py: init_langfuse at startup, shutdown on teardown
- redis_consumer.py: trace_span around journey_start/message/agent_trigger
- agent_runner.py: thread langfuse_handler through classify + processing LLM
- journey.py: thread langfuse_handler through _call_llm_with_tools
- llm.py: accept callbacks param, forward to LLM constructors
- requirements.txt: add langfuse>=3.0.0

services/batch-agent/app/llm.py

@@ -41,6 +41,7 @@ def get_llm(
     *,
     model: str | None = None,
     temperature: float = 0,
+    callbacks: list | None = None,
 ) -> ChatOpenAI | ChatLiteLLM:
     model = model or settings.LLM_MODEL
 
@@ -48,12 +49,13 @@ def get_llm(
         os.environ.setdefault("GITHUB_COPILOT_TOKEN_DIR", settings.GITHUB_COPILOT_TOKEN_DIR)
 
     if "/" in model:
-        return ChatLiteLLM(model=model, temperature=temperature)
+        return ChatLiteLLM(model=model, temperature=temperature, callbacks=callbacks)
 
     return ChatOpenAI(
         model=model,
         temperature=temperature,
         api_key=_api_key_for_model(model),
+        callbacks=callbacks,
     )