setup.sh: register SSO + proxy hostnames as Host records in the proxy

The proxy routes every hostname it serves purely off a Host record
(ops/nginx_conf/proxy.conf has no default/self route — targetinfo.lua
does a Redis lookup per request, full stop). Nothing created these for
the SSO's own UI or the proxy's own management UI, so on a fresh
install https://<SSO_HOST> and https://<PROXY_HOST> both 404 despite
setup.sh's summary claiming they're "fronted by the proxy under TLS".

Add a step after the proxy is healthy that runs a short script inside
the proxy container calling its Host model directly (no HTTP API call,
since no authenticated session exists yet at this point in the run):
- <SSO_HOST> -> sso-manager:3001 (the Docker service)
- <PROXY_HOST> -> 127.0.0.1:3000 (the proxy's own management app)

Both created with sso_enabled: false — each app already gates its own
login, and SSO-gating the SSO's own login page would be circular.
Idempotent: skips a host that already exists.

docs/quickstart.md

@@ -89,7 +89,10 @@ What happens:
    service account, your first admin, and the proxy's OAuth client, and writes
    the generated client id + secret into `./config/proxy-secrets.js`.
 4. Builds + starts **proxy**, waits for `/health`.
-5. Prints your first-admin login + the public URLs.
+5. Registers `<SSO_HOST>` and `<PROXY_HOST>` as Host records in the proxy —
+   every hostname the proxy serves, including its own UI and the SSO's,
+   needs one of these or it 404s. Idempotent.
+6. Prints your first-admin login + the public URLs.
 
 The first run builds two Docker images (a few minutes). Subsequent runs are
 fast.