Document org repository landscape for contributors

[BrendenWalker]

Purpose

Add additional documentation for contributors. I find it's easiest to get started contributing to any project by exploring and adding useful docs, simple stuff that's not going to break anything.

Hope this is helpful.

Summary

• Add a Repository landscape section to CONTRIBUTING.md after Workflow, aimed at new contributors who need to know which org repo to target.
• Includes a relationship diagram, a where-to-contribute table, plugin tier overview (core vs org vs community), and brief rationale for the multi-repo layout.

Test plan

• Read through CONTRIBUTING.md on GitHub preview — links and mermaid render correctly
• Confirm plugin tier list matches current plugins/ in core and build-common.sh in desktop

Summary by CodeRabbit

• Documentation
  • Added a new repository landscape section with a visual overview of the project’s repo structure.
  • Included a contribution guide showing where different types of changes should be submitted.
  • Documented plugin tiers and their expected locations/governance.
  • Added a brief explanation of why the project is split across multiple repositories.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a new "Repository landscape" section to CONTRIBUTING.md, including a mermaid diagram of repo relationships, a "Where to contribute" routing table, plugin tier definitions (Core/Org/Community), and a "Why multi-repo?" rationale.

Changes

Documentation update

Layer / File(s)	Summary
Repository landscape section CONTRIBUTING.md	Adds mermaid diagram of repo/service relationships, a contribution routing table, plugin tier definitions, and multi-repo rationale with an "Unsure?" guidance note.

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: documenting the repository landscape for contributors.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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_{Comment @coderabbitai help to get the list of available commands.}