Add `Add issue to project` workflow

[ColinDaglish]

Summary

Add a GitHub Actions workflow to automatically add newly opened issues to the relevant GitHub Project.

Why

Issues are not automatically captured by a project when they originate from multiple repositories. This workflow ensures newly opened issues are consistently added to the team project board without manual intervention.

Using a PROJECT_URL repository variable also makes the workflow reusable across repositories without hard-coding the project.

Proposed workflow

name: Add issue to project

on:
  issues:
    types: [opened]

permissions: {}

jobs:
  add-to-project:
    name: Add issue to project
    runs-on: ubuntu-latest
    steps:
      - name: Validate repository variable
        run: |
          if [[ -z "${{ vars.PROJECT_URL }}" ]]; then
            echo "❌ PROJECT_URL repository variable is not set"
            echo ""
            echo "Required Action:"
            echo "1. Go to: https://github.com/${{ github.repository }}/settings/variables"
            echo "2. Click 'New repository variable'"
            echo "3. Set Name: PROJECT_URL"
            echo "4. Set Value: https://github.com/orgs/[ORG_NAME]/projects/[PROJECT_NUMBER]"
            echo "5. Click 'Add variable'"
            echo ""
            exit 1
          fi

      - name: Generate app token
        id: app-token
        uses: actions/create-github-app-token@bcd2ba49218906704ab6c1aa796996da409d3eb1 # v3.2.0
        with:
          client-id: ${{ secrets.PROJECT_HANDLER_BOT_APP_ID }}
          private-key: ${{ secrets.PROJECT_HANDLER_BOT_PEM }}
          owner: ${{ github.repository_owner }}

      - uses: actions/add-to-project@5afcf98fcd03f1c2f92c3c83f58ae24323cc57fd # v2.0.0
        with:
          project-url: ${{ vars.PROJECT_URL }}
          github-token: ${{ steps.app-token.outputs.token }}

Acceptance criteria

• Newly opened issues are automatically added to the project specified by PROJECT_URL.
• The workflow fails with a clear message if PROJECT_URL is not configured.
• Existing PROJECT_HANDLER_BOT_APP_ID and PROJECT_HANDLER_BOT_PEM secrets are used.
• Actions are pinned to the specified commit SHAs.
• A test issue confirms the workflow successfully adds an issue to the project.