Migrate: Replace validate-design-md.sh with JavaScript

[ashleyshaw]

Overview

Migrate skills/design-md-agent/design-md-generator/scripts/validate-design-md.sh from Bash to JavaScript with Jest test coverage.

Current Implementation

The script validates DESIGN.md files by:

• Locating the design.md CLI from various sources (installed command, local repo, npx package, or zip files)
• Running spec and lint checks against the DESIGN.md file
• Generating a Markdown report with validation results
• Performing manual checks (frontmatter, required headings, filename)

Requirements

• Create scripts/design-md-agent/validateDesignMd.js equivalent
• Support environment variables: DESIGN_MD_FILE, DESIGN_MD_REPORT, DESIGNMD_REPO_PATH, DESIGNMD_CLI_CMD
• CLI detection strategy (command, local repo, npx fallback, zip extraction)
• Report generation (Markdown format with summary and manual checks)
• Jest tests covering all major paths
• Error handling for missing files and CLI unavailability
• Remove validate-design-md.sh after verification

Related

Part of #[bash-to-js-migration-epic] - Remove all shell scripts from the codebase

[linear-code]

LS-800