feat: migrate CI from CircleCI to GitHub Actions (#310)

Add comprehensive GitHub Actions CI workflow that matches CircleCI functionality:
- Node.js 20.17 environment setup
- MongoDB 7.0 service container
- Full test suite (prettier, eslint, package.json check, unit tests)
- Production build verification

Update README badge to show GitHub Actions CI status instead of CircleCI.

This provides better integration with GitHub repository and consolidates
CI/CD on a single platform alongside existing deployment automation.

Relates to #281

Author: TooAngel

.circleci/config.yml

@@ -0,0 +1,39 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+
+    services:
+      mongodb:
+        image: mongo:7.0
+        ports:
+          - 27017:27017
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20.17'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run tests
+        run: npm test
+        env:
+          MONGO_URL: mongodb://127.0.0.1:27017/worlddriven_test
+
+      - name: Build
+        run: npm run build

.github/workflows/ci.yml

@@ -1,6 +1,6 @@
 # Worlddriven Core
 
-[![CircleCI](https://circleci.com/gh/TooAngel/worlddriven.svg?style=svg)](https://circleci.com/gh/TooAngel/worlddriven)
+[![CI](https://github.com/TooAngel/worlddriven/actions/workflows/ci.yml/badge.svg)](https://github.com/TooAngel/worlddriven/actions/workflows/ci.yml)
 [![Discord](https://img.shields.io/discord/496780499059572756?logo=discord&logoColor=white&label=Discord&color=7289da)](https://discord.gg/RrGFHKb)
 [![Code Climate Maintainability](https://api.codeclimate.com/v1/badges/ec4136b6d2eeff72f192/maintainability)](https://codeclimate.com/github/TooAngel/worlddriven/maintainability)