feat(deploy): add HAProxy blue/green stack for zero-downtime relay updates

[Ferryx349]

Description

This pr adds an alternative production topology: two relay containers (nostream-blue,nostream-green) behind HAProxy on 127.0.0.1:8008, and a script that replaces them one at a time.

• deploy/haproxy/haproxy.cfg :- round-robin across both relays, /readyz health checks, and option redispatch so a request that fails on a dying backend is retried on the other one rather than returned to the client.
  A resolvers docker block re-resolves backend names against Docker's embedded DNS every 2s, so a recreated container's new IP is picked up; init-addr libc,none lets HAProxy boot before the relays are resolvable.
• deploy/docker-compose.haproxy.yml :- HAProxy plus the two relays, sharing one YAML anchor. Postgres, Redis, and the migrate job are unchanged from docker-compose.prod.yml. Relays get stop_grace_period: 45s so the
  WS_DRAIN_TIMEOUT_MS drain finishes before Docker escalates to SIGKILL.
• deploy/rolling-relay-recreate.sh :- stops one relay, waits for its replacement to report healthy via up --wait, then moves to the second.
• deploy/README.md — install and update procedure.docker-compose.prod.yml and the single-relay flow are untouched; operators opt in by using the new compose file.

Related Issue

Closes:- #776 and Relates to #773

Motivation and Context

How Has This Been Tested?

• docker compose -f deploy/docker-compose.haproxy.yml config parses, and both relays correctly inherit depends_on, healthcheck, and stop_grace_period from the shared anchor
• haproxy -c -f haproxy.cfg against haproxy:3.0-alpine exits 0. It emits two [NOTICE] lines about unresolvable backends when run outside the Compose network, which is the expected init-addr libc,none path — HAProxy parks the
  servers and boots instead of aborting
• Not yet exercised against a live stack; needs a sandbox run of rolling-relay-recreate.sh with a WebSocket client connected to confirm no dropped requests during cutover.

Screenshots (if appropriate):

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• I added a changeset, or this is docs-only and I added an empty changeset.
• All new and existing tests passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 967d4af

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
nostream	Minor

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