feat: split auth domain — Logto gets dedicated AUTH_HOST

Support separate auth domain (e.g. auth.cameleer.io) for Logto while
keeping the SaaS app on PUBLIC_HOST (e.g. app.cameleer.io). AUTH_HOST
defaults to PUBLIC_HOST for backward-compatible single-domain setups.

- Logto routing: Host(AUTH_HOST) replaces PathPrefix('/') catch-all
- Root redirect moved from traefik-dynamic.yml to Docker labels with
  Host(PUBLIC_HOST) scope so it doesn't intercept auth domain
- Self-signed cert generates SANs for both domains
- Bootstrap Host header uses AUTH_HOST for Logto endpoint validation
- Spring issuer-uri and oidcissueruri use new authhost property
- Both installers (sh + ps1) prompt for AUTH_HOST in expert mode

Local dev: AUTH_HOST=auth.localhost (resolves to 127.0.0.1, no hosts file)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/cameleer-traefik/traefik-dynamic.yml

@@ -1,21 +1,3 @@
-http:
-  routers:
-    root-redirect:
-      rule: "Path(`/`)"
-      priority: 100
-      entryPoints:
-        - websecure
-      tls: {}
-      middlewares:
-        - root-to-platform
-      service: saas@docker
-  middlewares:
-    root-to-platform:
-      redirectRegex:
-        regex: "^(https?://[^/]+)/?$"
-        replacement: "${1}/platform/"
-        permanent: false
-
 tls:
   stores:
     default: