Replaces the paywalled bitnamilegacy app with the official discourse/discourse
image behind Traefik (HTTP-only via an install-ssl override; sidekiq is internal
so its service is dropped). DB is reused as-is; uploads migrate from a legacy
bitnami volume via an idempotent, non-destructive runit hook. db keeps
pgvector/pgvector:pg17 with the install-user-aware pg_upgrade entrypoint, plus
db/redis healthchecks and updated README metadata (lint R002/R007).
Verified on cctest: fresh install, upgrade-from-bitnami-pg17, and
upgrade-from-bitnami-pg13 (incl. 13->17) all serve with data intact.
Upstream marks discourse/discourse experimental; hold prod cutover.
Recipe 0.8.1+3.5.0 -> 1.0.0+3.5.3 (major: new image, env/volume/port changes).
