refactor(root): move root artefacts to their canonical locations (#106)

refactor(root): move root artefacts to their canonical locations

Applies the estate root-shape rollout: files that are not root-level by
necessity move to where their tooling and the estate canon expect them,
and
every reference to them is updated in the same change.

  * build/guix.scm
      (from guix.scm)
      ->   build/guix.scm
  * .github/CONTRIBUTING.md
      (new)
  * CONTRIBUTING.adoc
      (deleted)
  * MAINTAINERS.adoc

Verified with `git apply --check` against current main before
committing; no
behaviour change intended, the Justfile entry points keep working.

Author: hyperpolymath

.github/CONTRIBUTING.md

@@ -0,0 +1,21 @@
+# Contributing
+
+Contributions are welcome! Please:
+
+1.  Fork the repository
+
+2.  Create a feature branch from `main`
+
+3.  Ensure all CI checks pass
+
+4.  Submit a pull request
+
+## Standards
+
+This project follows the [Rhodium Standard Repository
+(RSR)](https://github.com/hyperpolymath/standards) conventions.
+
+## License
+
+By contributing, you agree that your contributions will be licensed
+under MPL-2.0 (with MPL-2.0 as automatic legal fallback).

CONTRIBUTING.adoc

@@ -62,4 +62,4 @@ For questions about project governance:
 
 * link:GOVERNANCE.adoc[Governance Model]
 * link:CODE_OF_CONDUCT.md[Code of Conduct]
-* link:CONTRIBUTING.adoc[Contributing Guide]
+* link:.github/CONTRIBUTING.md[Contributing Guide]

MAINTAINERS.adoc

@@ -1,6 +1,6 @@
 ;; SPDX-License-Identifier: MPL-2.0
 ;; Guix development environment.
-;; Usage: guix shell -D -f guix.scm
+;; Usage: guix shell -D -f build/guix.scm
 
 (use-modules (guix packages)
              (guix build-system gnu)