feat: add reusable PR Slack notification workflow

[tomassrnka]

Summary

• Reusable workflow that any e2b-dev repo can call to post new PRs to a Slack channel
• Tags a configurable Slack user group (e.g. @pr-infra, @pr-belt)
• Each repo just needs a ~10 line caller workflow + two repo variables

Usage in a repo

# .github/workflows/pr-slack-notify.yml
name: Post PR to Slack
on:
  pull_request_target:
    types: [opened, ready_for_review]
jobs:
  notify:
    uses: e2b-dev/.github/.github/workflows/pr-slack-notify.yml@main
    secrets:
      SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
    with:
      channel_id: ${{ vars.SLACK_CHANNEL_ID }}
      review_group: ${{ vars.SLACK_REVIEW_GROUP }}

Repo variables needed:

• SLACK_CHANNEL_ID — the #code-review-requests channel ID
• SLACK_REVIEW_GROUP — Slack user group ID (e.g. for @pr-infra)

Test plan

• Merge this PR
• Set up a caller workflow in infra repo (separate PR)
• Trigger via workflow_dispatch or open a test PR
• Verify message in #code-review-requests

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Introduces a new GitHub reusable workflow that posts to Slack using a bot token; misconfiguration or token/channel issues could cause missed/incorrect notifications but does not affect production code paths.

Overview
Adds a reusable GitHub Actions workflow, pr-slack-notify.yml, that can be workflow_call’d by other repos to post new PR notifications to Slack, tagging a configurable user group.

Includes a small Node-based action (.github/actions/pr-slack-notify) that installs @slack/web-api and posts the message, skipping draft PRs, supporting manual triggers via env-provided PR fields, and escaping Slack mrkdwn in PR titles to avoid mention/injection.

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[cursor]

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