docs/example: docker compose for Zeek + Blueflow + Postgres + Redis

[xnorkl]

Goal — Provide a standalone example docker-compose.yml (path TBD, e.g. examples/ or docker/hackathon/) that a newcomer can run to bring up:

• Zeek (repo's Zeek image / Dockerfile — document build context),
• Blueflow (app container built from repo root Dockerfile),
• PostgreSQL (persistent DB for Django),
• Redis (for runtime wiring Blueflow expects in this demo — broker/cache/etc.; align env vars with settings),

without relying on compose profiles or stub/receiver naming patterns.

Out of scope

• Automated CI verification or extending docker/verify.py here — validation stays with the test harness in the other repo.
• Choosing the hackathon PCAP or naming HL7/DICOM — fixture remains TBD; compose should accept PCAP_DIR / PCAP_FILE (or mounted volume) with sane defaults documented.

Deliverables

• One example compose file + minimal README beside it: prerequisites (Docker), build/start commands, env placeholders (DATABASE_URL, Redis/CELERY env if applicable), ports, and where logs/data volumes land.
• Document service dependency order (e.g. depends_on + healthchecks for Postgres/Redis before Blueflow migrates/starts).
• Wire Zeek → Blueflow in whatever form this milestone adopts (HTTP ingest, shared logs, etc.) — keep wording neutral so feat: Zeek conn telemetry → Blueflow #49 can finalize the pipe without rewriting compose twice.

Related

• feat: Zeek conn telemetry → Blueflow #49 — ingest path / Zeek output shape
• hackathon: REST routes required for PCAP demo compose #116 — HTTP routes the example expects