feat: add agent skills for Claude Code and GitHub Copilot

[Copilot]

Why?

Enable autonomous skill invocation for SDD workflows in Claude Code and GitHub Copilot agents, complementing existing slash command installation.

What Changed?

Agent Skills Structure

• .claude/skills/ - Claude Code skill definitions (4 skills)
• .github/skills/ - GitHub Copilot skill definitions (4 skills)
• Each skill directory contains SKILL.md with existing prompt content

Skills Installed

• sdd-1-generate-spec - Spec generation with workflow guidance
• sdd-2-generate-task-list - Task breakdown from specs
• sdd-3-manage-tasks - Guided implementation with verification
• sdd-4-validate-implementation - Spec validation with proof artifacts

Documentation Updates

• Added "Option B: Install as Agent Skills" to README installation section
• Installation commands include mkdir -p for idempotent setup
• Linked to official Claude Code and GitHub Copilot skills documentation
• Added README files to both skill directories

Installation

# Claude Code (user-wide)
mkdir -p ~/.claude/skills
cp -r .claude/skills/* ~/.claude/skills/

# GitHub Copilot (project-specific)
mkdir -p /path/to/project/.github
cp -r .github/skills /path/to/project/.github/

Additional Notes

• Linked relevant spec/task IDs (problem statement references)
• Ran linters/hooks: pre-commit run --all-files
• Updated docs (README.md and skill READMEs)

Original prompt

Create skill installation for this workflow and update docs supporting Claude Code and GitHub Copilot

https://code.claude.com/docs/en/skills

https://github.blog/changelog/2025-12-18-github-copilot-now-supports-agent-skills/

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

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