ci: Sync issues to a target GitHub project #1235

Summary

A GitHub Actions workflow that syncs issue lifecycle events from this repo
to a target GitHub Project in another organization.

Goals

• Automatically add an issue to a target GitHub Project when it is opened
• Automatically set the project item Status to Done when the issue is closed
• Support cross-org project targeting with no custom fields required
• Keep configuration minimal via a single repo variable and secret

Proposed Solution

A workflow triggered on issues: [opened, closed] that uses the GitHub GraphQL
API to:

1. On opened — add the issue to the target project via addProjectV2ItemById,
   establishing a native link between the project item and the source issue
2. On closed — find the project item by matching content.node_id to the
   issue's node ID, then update its Status field to Done

Configuration:

• PSYNC_TARGET (repo variable) — target project in org:project_number
  format (e.g. my-org:1)
• PSYNC_PAT (repo secret) — PAT with project and read:org scopes on
  the target org

Non-goals

• Does not sync issue edits, label changes, or assignee updates to the project
• Does not create or manage custom fields in the target project
• Does not support GitHub Projects v1 (classic)