Run `mgf-fed start` and follow what it prints EXACTLY.

`start` is the federation **front-door** — one command for every onboarding
case, so you don't have to know which prompt you need up front. It is
print-only (it never edits files): it auto-detects when this repo is already a
federation member and prints the **sync** prompt; otherwise it prints a short
scenario menu. Pick by intent and re-run with `--mode`:

- `mgf-fed start --mode new` — an **empty** repo that will become a new `mgf-*` member
- `mgf-fed start --mode onboard` — **existing** external code that will JOIN as a member
- `mgf-fed start --mode sync` — an **existing member**, bring it current
- `mgf-fed start --mode adopt` — adopt the MGF standards but stay **independent**

`mgf-fed start --list` reprints the menu. The four cases also have dedicated
commands: `/new-project`, `/onboard`, `/sync`, `/adopt`.

If `mgf-fed start` reports that the corpus is not installed, run:

    pip install -U 'mgf-common[standards]'

then re-run it. (The standards corpus is an optional Codeberg-only extra; a
plain `mgf-common` install does not carry it.)
