refactor: rebrand from net.siegeln to io.cameleer

Institutionalize the product identity ahead of public release:

- Java package: net.siegeln.cameleer.saas → io.cameleer.saas (109 files)
- Maven groupId: net.siegeln.cameleer → io.cameleer
- Public image defaults: gitea.siegeln.net/cameleer/ → registry.cameleer.io/cameleer/
- Updated docs (architecture, user-manual, HOWTO, runtime-loader README)
- Updated CLAUDE.md path references

Internal build infra (CI workflows, .gitmodules, npm registry, Maven repo)
intentionally kept at gitea.siegeln.net — code stays on internal Gitea.

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

docker/runtime-loader/README.md

@@ -12,8 +12,8 @@ CI (`.gitea/workflows/ci.yml`, `docker` job, "Build and push runtime-loader
 image" step) builds and pushes this image on every main / feature-branch
 push. Manual build for local testing:
 
-    docker build -t gitea.siegeln.net/cameleer/cameleer-runtime-loader:<tag> .
-    docker push gitea.siegeln.net/cameleer/cameleer-runtime-loader:<tag>
+    docker build -t registry.cameleer.io/cameleer/cameleer-runtime-loader:<tag> .
+    docker push registry.cameleer.io/cameleer/cameleer-runtime-loader:<tag>
 
 ## Contract (consumed by cameleer-server)