merge: compose env passthrough for dispatch participant

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.yml

@@ -36,6 +36,13 @@ x-common-env: &common-env
   APP_WORK_DIR: /data/work
   CORS_ALLOWED_ORIGINS: ${CORS_ALLOWED_ORIGINS:-http://localhost:5273,http://localhost:4173}
   API_KEY: ${API_KEY:-}
+  INGEST_API_KEY: ${INGEST_API_KEY:-}
+  # Dispatch participant (D4 bus): values come from the gitignored .env.
+  DISPATCH_ENABLED: ${DISPATCH_ENABLED:-false}
+  DISPATCH_API_URL: ${DISPATCH_API_URL:-}
+  DISPATCH_API_KEY: ${DISPATCH_API_KEY:-}
+  DISPATCH_PARTICIPANT_CODE: ${DISPATCH_PARTICIPANT_CODE:-legacyhub}
+  DISPATCH_TIMEOUT_SECONDS: ${DISPATCH_TIMEOUT_SECONDS:-5}
 
 # Module-contract isolation: data services live on the internal-only
 # legacyhub_db network (the same name docker-compose.teamhub.yml uses, so the