feat: auto-assign all PRs to maintainer

[stdNullPtr]

Summary

Add GitHub Actions workflow to automatically assign all new pull requests to the maintainer.

Changes

• Added .github/workflows/auto-assign.yml
• Triggers on pull_request: opened events
• Uses actions/github-script@v7 to assign PRs to stdNullPtr
• Requires only pull-requests: write permission

Implementation Details

on:
  pull_request:
    types: [opened]

The workflow uses GitHub's REST API to add the maintainer as an assignee:

github.rest.issues.addAssignees({
  owner: context.repo.owner,
  repo: context.repo.repo, 
  issue_number: context.issue.number,
  assignees: ['stdNullPtr']
});

This ensures consistent assignment of all incoming pull requests for review tracking.