* docs(readme): document image tag convention (edge vs latest) Add Image Tags section explaining :latest (stable releases), :edge (staging builds from main), semver tags, and per-build staging tags. Helps self-hosters pick the right image version. * fix(ci): use Docker healthcheck status instead of curl for deploy verification The staging VPS doesn't expose API/Web ports to the host (only Caddy ports 80/443 are exposed). The health check was curling 127.0.0.1:3000 which is unreachable, causing every deploy to fail and trigger rollback. Now uses `docker inspect` to check Docker's own healthcheck status, which works regardless of port exposure. Also increases API timeout to 90s to account for the healthcheck start-period (30s) and includes container logs in failure output for easier debugging.