chore(gh-aw): Create workflows/ directory with squad.md + shared/squad.md #1620

Create workflows/ Directory Structure

Part of #1612 (Squad Agentic Workflows epic).
This is the foundational repo structure that all other issues depend on.

Overview

Create the directory structure in our repo that gh-aw's add command will resolve from. This is the distribution surface — the files users pull when they install Squad via gh-aw.

Directory Structure

workflows/
├── squad.md              # The unified /squad workflow
└── shared/
    └── squad.md          # Bootstrap component (activation job)

Distribution

Users install via:

gh aw add bradygaster/squad/workflows/squad.md@latest

This resolves to workflows/squad.md in our repo at the latest tag/branch.

File Responsibilities

Notes

• These files follow gh-aw's Markdown-based workflow format (not standard YAML GitHub Actions)
• The shared/ directory is gh-aw's convention for reusable components
• Version resolution (@latest, @v1, etc.) is handled by gh-aw infrastructure
• Our CI should validate these files remain syntactically correct

Acceptance Criteria

• workflows/squad.md exists and is valid gh-aw workflow syntax
• workflows/shared/squad.md exists and is valid gh-aw component syntax
• gh aw add bradygaster/squad/workflows/squad.md@latest resolves correctly
• Directory structure follows gh-aw conventions for shared components
• Files are linted/validated in CI (if gh-aw provides a validator)
• README or docs reference the installation command