D-045 — the setup gate is now `config.setup`, not the peer/SSH tunnel:
- setup: true -> /setup serves the wizard (the code form first when
`setup_code` is set, via the existing D-044 gate);
GET / points at the wizard; every other route -> 404.
- setup: false + no admin -> LOCKED: GET / and /setup render an "enable
setup" boilerplate; every other route -> 404; the
wizard is not claimable.
- completion -> writes `setup: false` and creates the admin.
`setup_code` is now OPTIONAL: blank => Gate.Required() false => the toggle
alone admits; set => required (reusing the unlock cookie/fingerprint/
redaction/rate-limit). The peer/tunnel gate is retired: `httpx.
SetupRequestAllowed` and `httpx.IsLoopbackIP` are deleted; the XFF/XFP
handling is kept for the client IP and the Secure/__Host- cookies + HSTS
(A6/A11/D-043). The !bootstrapped() fail-safe becomes the locked predicate,
latched at startup.
New door seams: Deps.LockedMode and SetupGate.{Required,CodeForm,Landing,
Locked}; the Gate renders three first-run pages. The startup banner states
the mode and prints the code only when required.
Tests cover the three states, the boilerplate, the code optionality and the
unlock mechanics; live-smoked end to end (locked / wizard / code form /
full bootstrap -> setup: false).