Configure repositories for cross-repo integration: Copilot instructions + reusable workflows

[Copilot]

Description

Establishes the shared infrastructure needed for all lippytm repositories to operate consistently as standalone projects and as a cohesive ecosystem. Adds Copilot coding agent instructions, a reusable CI workflow callable by any sibling repo, and a cross-repo sync workflow to propagate standard changes.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 📚 Documentation update
• 🔨 Build/CI updates

Related Issue(s)

Changes Made

• .github/copilot-instructions.md — Copilot agent instructions covering architecture, code conventions (CommonJS, async/await, React hooks, Python type hints), security rules (rate limiting, auth middleware, XML escaping), environment variable policy, and cross-repo integration guide. Addresses issue ✨+Set+up+Copilot+instructions #11.

• .github/workflows/reusable-ci.yml — Reusable workflow any sibling repo can invoke with one line to inherit standard CI checks: Trivy security scan (pinned v0.30.0), ESLint, Ruff, dependency audit (npm + pip-audit), and README/.env.example presence validation.

  # In any sibling repo's .github/workflows/ci.yml:
  jobs:
    shared-ci:
      uses: lippytm/AI-Time-Machines/.github/workflows/reusable-ci.yml@main
      secrets: inherit

• .github/workflows/cross-repo-sync.yml — Fires on pushes to main that touch shared files (.github/workflows/, config/, .env.example) and dispatches a repository_dispatch event to listed sibling repos. Requires GITHUB_PAT secret (repo + workflow scopes); skips gracefully when absent. Populate SIBLING_REPOS in the workflow file with your repo names to activate.

Testing

• Manual testing completed — YAML validated via python3 -c "import yaml; yaml.safe_load(...)" for both workflow files
• No breaking changes — all additions are net-new files; no existing workflows modified

Screenshots (if applicable)

N/A

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Additional Context

To fully activate cross-repo sync across all 20 repositories:

1. Create a PAT with repo + workflow scopes at https://github.com/settings/tokens
2. Add it as GITHUB_PAT in each repo's Settings → Secrets and variables → Actions
3. Add sibling repo names to the SIBLING_REPOS block in cross-repo-sync.yml and push to main