refactor: move installer to dedicated repo, wire as git submodule

The installer (install.sh, templates/, bootstrap scripts) now lives in
cameleer/cameleer-saas-installer (public repo). Added as a git submodule
at installer/ so compose templates remain the single source of truth.

Dev compose is now a thin overlay (ports + volume mount + dev env vars).
Production templates are chained via COMPOSE_FILE in .env:
  installer/templates/docker-compose.yml
  installer/templates/docker-compose.saas.yml
  docker-compose.yml (dev overrides)

No code duplication — fixes to compose templates go to the installer
repo and propagate to both production deployments and dev via submodule.

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

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "installer"]
+	path = installer
+	url = https://gitea.siegeln.net/cameleer/cameleer-saas-installer.git