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>

docker-compose.yml

@@ -86,6 +86,8 @@ services:
     environment:
       <<: *app-env
       SERVICE_NAME: gateway
+    env_file:
+      - .env.observability
     command: uvicorn services.gateway.app:app --host 0.0.0.0 --port 8000 --reload --no-access-log
     ports:
       - "8000:8000"
@@ -128,6 +130,8 @@ services:
     environment:
       <<: *app-env
       SERVICE_NAME: fraud
+    env_file:
+      - .env.observability
     command: uvicorn services.fraud.app:app --host 0.0.0.0 --port 8002 --reload --no-access-log
     ports:
       - "8002:8002"