feat(develop): parallel test servers via eo.sh

[juliusknorr]

Adds develop/eo.sh to run multiple isolated DocumentServer test instances in parallel from the prebuilt multi-arch :latest-dev image, no full docker build required. Useful for quickly verifying submodule changes (incl. by coding agents) and for testing several branches/worktrees at once.

Each instance is a single self-contained container (its own Postgres/Redis/RabbitMQ/Nginx/supervisord) that mounts the current git working tree at /develop, so the existing in-container make targets rebuild local changes in place.

eo.sh up [--force] <name> [port]   # start; auto host port; waits for /healthcheck; prints URLs
eo.sh build <name> <make-target>   # web-apps-dev | sdkjs | server/docservice | core/x2t | …
eo.sh exec <name> [cmd…]           # shell/command inside (TTY-aware)
eo.sh logs <name>                  # follow logs
eo.sh ls                           # instances with status, port, URL, mount path
eo.sh down <name>… | --all         # stop & remove

Instances run with JWT enabled (shared dev secret), EXAMPLE_ENABLED and WOPI_ENABLED, so the bundled example app works and documents open. up prints create-new editor URLs for all document types.

Also corrects a stale develop/README.md note (a multi-arch :latest-dev incl. arm64 is published, so make pull works on Apple Silicon) and documents the new workflow.

Verification

• Multiple instances run concurrently on distinct auto-assigned ports; healthchecks pass; example editor opens a document end-to-end.
• eo.sh build … web-apps-dev runs a real in-container build and reloads nginx.
• bash -n + shellcheck clean; kept bash 3.2 compatible (macOS system bash).