docs: fix developer-guide route registration + CONTRIBUTING dead links

developer-guide: RPC dispatch moved from mod.rs handle_rpc_call to
dispatcher.rs dispatch() long ago — the registration instructions now point
at the real file; module tree updated (package/, federation/, mesh/ are
directories; mesh is tri-protocol); roadmap pointer loop/plan.md → docs/ROADMAP.md.
CONTRIBUTING: docs/development-setup.md never existed → developer-guide.md;
GitHub-specific fork URL generalized to the Gitea instance.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -8,9 +8,9 @@ Be respectful. We follow the [Contributor Covenant](https://www.contributor-cove
 
 ## Getting Started
 
-1. Fork the repository
-2. Clone your fork: `git clone https://github.com/YOUR_USERNAME/archy.git`
-3. Set up the dev environment (see `docs/development-setup.md`)
+1. Fork the repository on the project's Gitea instance
+2. Clone your fork: `git clone <your-fork-url>/archy.git`
+3. Set up the dev environment (see `docs/developer-guide.md`)
 4. Create a feature branch: `git checkout -b feature/your-feature`
 
 ## Development Setup