feat(me): add codebase design skill

[baleen37]

Summary

• Add the upstream codebase-design skill under the flat bstack skill layout.
• Include DEEPENING.md and DESIGN-IT-TWICE.md companion references.
• Advertise the skill in the me plugin README.

Validation

• bun run check:codex
• bash tests/run-all-tests.sh
• Upstream pinned-file comparison
• git diff --cached --check

Summary by CodeRabbit

• New Features
  • Added the codebase-design workflow to the planning guidance.
  • Added guidance for designing deeper modules, selecting dependency boundaries, and testing observable behavior.
  • Added a “Design It Twice” workflow for comparing multiple interface designs before implementation.
• Documentation
  • Expanded design terminology and principles covering interfaces, adapters, seams, module depth, and testability.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: ec4e131e-c94c-4459-ac03-81532add52e8

📥 Commits

Reviewing files that changed from the base of the PR and between 4607217 and a7dcfeb.

📒 Files selected for processing (4)

• plugins/me/README.md
• plugins/me/skills/codebase-design/DEEPENING.md
• plugins/me/skills/codebase-design/DESIGN-IT-TWICE.md
• plugins/me/skills/codebase-design/SKILL.md

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📝 Walkthrough

Walkthrough

The PR adds the codebase-design skill to the me plugin. It documents deep modules, dependency seams, testability, dependency deepening, and parallel exploration of alternative interfaces.

Changes

Codebase design skill

Layer / File(s)	Summary
Skill foundation and workflow wiring plugins/me/skills/codebase-design/SKILL.md, plugins/me/README.md	Defines deep-module terminology, interface and testability principles, design relationships, rejected framings, related guidance, and the Plan workflow entry.
Dependency deepening guidance plugins/me/skills/codebase-design/DEEPENING.md	Classifies dependency types and documents ports, adapters, seams, adapter-count criteria, and interface-level tests.
Alternative interface design plugins/me/skills/codebase-design/DESIGN-IT-TWICE.md	Defines constraint framing, parallel design briefs, required analyses, design comparison, and recommendations based on depth, locality, and seam placement.

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

Possibly related PRs

• baleen37/bstack#649: Updates workflow documentation in plugins/me/README.md.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/add-skill

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