feat: centralize reviewer assignment and update README

[Dorac]

Summary

• Rewrite assign_reviewers.yml as a reusable workflow (workflow_call), so all cp-* repos can call it instead of maintaining their own reviewer list
• Replace kentaro-m/auto-assign-action with actions/github-script — calls GitHub API directly, filters out PR author, no config file dependency
• Update README to reflect current workflow inventory with caller examples

Motivation

Slack bots (GitHub App / typo) only notify on individual reviewer assignment, not team group assignment. We want individual assignment but without maintaining the list in every repo. Now the list lives in one place — update assign_reviewers.yml here and all repos pick it up automatically.

How to migrate other repos

Replace the existing assign_reviewers.yml (and auto_assign.yml if present) with:

name: Assign Reviewers

on:
  pull_request:
    types: [ready_for_review, opened]

jobs:
  assign:
    uses: CoolBitX-Technology/cp-workflow-template/.github/workflows/assign_reviewers.yml@master

Test plan

• Open a PR in this repo and verify all 6 reviewers (minus the author) are assigned
• Verify Slack notification is received

🤖 Generated with Claude Code

PR Summary by Typo

Overview

This PR centralizes the logic for assigning reviewers to pull requests within a reusable GitHub Actions workflow and significantly updates the project's README.md to document this and other reusable workflows.

Key Changes

• The assign_reviewers.yml workflow was converted into a reusable workflow (workflow_call).
• The reviewer assignment mechanism was switched from a third-party action to a custom github-script to allow for more flexible logic, including excluding the PR author from the assigned reviewers.
• A hardcoded list of reviewers is now maintained directly within the assign_reviewers.yml workflow.
• The README.md was extensively updated to provide comprehensive documentation and usage examples for all reusable workflows, including the new assign_reviewers.yml.

Work Breakdown

Category	Lines Changed
New Work	151 (86.8%)
Churn	1 (0.6%)
Refactor	22 (12.6%)
Total Changes	174

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Static Code Review 📊

✅ All quality checks passed!

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AI Code Review 🤖

Files Reviewed: 2
Comments Added: 0
Lines of Code Analyzed: 196
Critical Issues: 0

PR Health: Excellent 🔥

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