[codex] Clarify dry-run and moonbuild history

[peter-jerry-ye]

Summary

• Update developer docs to describe moonbuild-rupes-recta as the current graph generator and moonbuild as a historical-name shared support crate.
• Clarify --dry-run output: paste-ready shell commands are the expected product direction, but current output does not fully satisfy that contract.
• Document privacy constraints for dry-run rendering: avoid leaking home directories, workspace roots, custom toolchain paths, and local caches unless users opt into raw paths.
• Document the git history behind dry-run path normalization and the graph-dump test hook.
• Replace stale virtual-package references to removed crates/moonbuild/src/gen/... files with current RR module references.

User-facing behavior

• Documentation only; no runtime behavior change.

Validation

• git diff --check
• stale-reference rg checks for removed legacy-generator paths
• checked new RR doc link targets exist

[semanticdiff-com]

Review changes with