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>

CLAUDE.md

@@ -21,7 +21,7 @@ Agent-server protocol is defined in `cameleer/cameleer-common/PROTOCOL.md`. The
 
 ## Key Packages
 
-### Java Backend (`src/main/java/net/siegeln/cameleer/saas/`)
+### Java Backend (`src/main/java/io/cameleer/saas/`)
 
 | Package | Purpose | Key classes |
 |---------|---------|-------------|