feat(landing): self-serve registration page via Drasl API (B1)

Add a static /register page (en/es/eu) that calls the Drasl REST API v2
directly from the browser: register -> login -> optional skin upload, all
in the pixel design. Guests never touch Drasl's own web UI.

Drasl config gains the pieces this needs:
- CORSAllowOrigins scoped to the apex (the API has no CORS until set;
  never "*").
- [RateLimit] for the now public-facing anonymous POST /users.
- [RegistrationNewPlayer] with RequireInvite driven by a new
  REGISTRATION_MODE (invite|open) .env flag.

REGISTRATION_MODE has two consumers from one key: render-config.sh derives
the TOML boolean for Drasl (drasl is TOML-only, no env), and the landing
build reads it to show/hide the invite-code field. render-config.sh halts
on any value other than invite/open.

Security verified against drasl source: anonymous POST /users cannot set
privileged fields (isAdmin/isLocked/chosenUuid/maxPlayerCount are gated on
callerIsAdmin in CreateUser), so browser-direct registration is safe.

Docs: plan/16-landing-registration.md captures the design + the B1 vs fork
decision; build-order, deploy, and the deploy skill wire REGISTRATION_MODE
and the landing-rebuild requirement (www/ is gitignored, not updated by a
git pull).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

drasl/config/config.toml.tmpl

@@ -1,6 +1,7 @@
 # Drasl config — password-login mode (NO Keycloak/OIDC for now).
 # TOML only (drasl has no env support). Rendered by tooling/render-config.sh
-# -> drasl/config/config.toml (gitignored). Only ${BASE_DOMAIN} is substituted.
+# -> drasl/config/config.toml (gitignored). Substitutes ${BASE_DOMAIN} and
+# ${REGISTRATION_REQUIRE_INVITE} (derived from REGISTRATION_MODE in .env).
 # Reached only via Caddy at auth.${BASE_DOMAIN}; drasl has no published host port.
 
 # Public scheme is HTTPS — the host nginx terminates TLS in front of caddy.
@@ -21,5 +22,27 @@ SignPublicKeys = false
 # Free-text owner label shown in the web UI (a string, not a table).
 ApplicationOwner = "Ulicraft"
 
+# New-account registration (username+password). RequireInvite is derived from
+# REGISTRATION_MODE in .env by render-config.sh: invite -> true, open -> false.
+# When true, non-admin callers (web UI + landing register form) must supply a
+# valid invite code; admins bypass. Mint codes via POST /drasl/api/v2/invites
+# with an admin api token.
+[RegistrationNewPlayer]
+Allow = true
+RequireInvite = ${REGISTRATION_REQUIRE_INVITE}
+
+# CORS: the landing register/account form (served from the apex) calls the
+# Drasl API from the browser. Without this the API has NO CORS headers and the
+# browser blocks every cross-origin call. Scope to the apex only — never "*",
+# which would let any site script the auth API. Echo backfills AllowMethods
+# (incl. PATCH/DELETE) and reflects requested headers (Content-Type/Authorization).
+CORSAllowOrigins = ["https://${BASE_DOMAIN}"]
+
+# Rate limit the now public-facing API (anonymous POST /users etc). Token
+# bucket; admins are exempt. Conservative for a 4-10 player server.
+[RateLimit]
+RequestsPerSecond = 5
+Burst = 10
+
 # OIDC block intentionally omitted for now (no Keycloak).
 # [[RegistrationOIDC]]  <- future task