Add workflow for org-managers to invite users to organization

[Copilot]

Adds a manually-triggered workflow that allows members of the "org-managers" team to send organization invitations to specified GitHub users via the REST API.

Implementation

• Workflow trigger: workflow_dispatch with required username input
• Authorization: Validates actor is member of "org-managers" team using /orgs/{org}/teams/{team}/members/{user} endpoint
• Input validation: Regex pattern ^[a-zA-Z0-9]([a-zA-Z0-9-]*[a-zA-Z0-9])?$ with 39-char limit
• API call: PUT /orgs/{org}/memberships/{username} with role='member'
• Permissions: Explicit contents: read only

Setup Requirements

1. Create "org-managers" team in organization
2. Add PAT_TOKEN secret with admin:org and read:org scopes

on:
  workflow_dispatch:
    inputs:
      username:
        description: 'GitHub username to add to the organization'
        required: true
        type: string

Workflow fails fast if actor lacks team membership or username format is invalid. No sensitive data logged in error messages.

Original prompt

On workflows, I would like to create a new github action workflow that is run manually, receiving a string input named "username". The workflow will then check that the user running it is a member of a specific group (lets call it "org-managers"), and if so, will attempt to add that user to the current organization via the Github REST API, using a PAT stored as a secret.

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