feat: sync GitHub issues to Yunxiao

[syzsunshine219]

Summary

Add a repository-local GitHub Actions workflow that synchronizes memmy-agent Issues and Pull Requests directly to the Yunxiao memmy project.

The workflow keeps deterministic CRUD synchronization separate from the coding agent path. It supports lifecycle events, preflight validation, dry-run backfill, and explicit backfill of historical open or closed items.

Mapping

• Yunxiao project: memmy
• Project ID: 1832b179386e24414d3891e244
• Parent directory: intentionally unset; the supplied viewIdentifier is a list view, not a work item parent ID
• Idempotency key includes the full GitHub repository, so Issue numbers cannot collide across repositories

Validation

• python3 -m unittest scripts/test_yunxiao_github_sync.py
• python3 -m py_compile scripts/yunxiao_github_sync.py
• npm exec vitest run tests/yunxiao-github-sync-workflow.test.ts tests/release-workflow.test.ts
• git diff --check

Repository configuration

Actions Variables for the memmy-agent repository have been set for the project, work item category/type, priority, and planned duration. YUNXIAO_TOKEN still needs to be added as an Actions Secret before enabling live synchronization; no placeholder credential was stored.