Propagate traces over HTTP and add Redis spans

setup_telemetry now instruments httpx and redis process-wide. Both patch
the client classes, so clients created at import time (gateway's
_proxy_client, common.redis_client) are covered too. httpx CLIENT spans
inject traceparent, so the downstream FastAPI SERVER spans join the
caller's trace. gateway and fraud get setup_telemetry, the FastAPI span,
and the OTLP auth header. All seven services now export traces.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/gateway/app.py

@@ -7,18 +7,27 @@ from fastapi import FastAPI, Request
 from fastapi.responses import FileResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel, field_validator
+from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
 
 from common.chaos_flags import ALL_FLAGS, get_flags, set_flag, set_profile
 from common.logging_config import configure_logging
 from common.settings import settings
+from common.telemetry import setup_telemetry
 
 from . import orchestrator
 from .orchestrator import UpstreamFailure
 
 SERVICE_NAME = "gateway"
 logger = configure_logging(SERVICE_NAME)
+setup_telemetry(service_name=SERVICE_NAME)
 app = FastAPI(title=SERVICE_NAME)
 
+FastAPIInstrumentor.instrument_app(
+    app,
+    excluded_urls="/healthz",
+    exclude_spans=["receive", "send"],
+)
+
 STATIC_DIR = Path(__file__).parent / "static"
 app.mount("/static", StaticFiles(directory=STATIC_DIR), name="static")