add multi-stage Docker build with CI support

- Add dev stage with xdebug for local development
- Add ci stage with composer dependencies for GitHub Actions
- Update docker-compose to target dev stage
- Add GitHub Actions workflow for continuous integration

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: pscheit

.github/workflows/continuous-integration.yml

@@ -0,0 +1,20 @@
+name: Continuous Integration
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    
+    steps:
+    - uses: actions/checkout@v4
+    
+    - name: Build Docker image
+      run: docker build -t webforge-utils-ci -f config/docker/php/Dockerfile --target ci .
+    
+    - name: Run PHPUnit tests
+      run: docker run --rm webforge-utils-ci ./vendor/bin/phpunit

config/docker/php/Dockerfile

@@ -1,4 +1,4 @@
-FROM php:8.4-fpm
+FROM php:8.4-fpm AS base
 
 RUN apt-get update && apt-get install -y git zip unzip
 
@@ -9,3 +9,11 @@ RUN mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini" \
 COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
 
 WORKDIR /app
+
+FROM base AS dev
+RUN pecl install xdebug && docker-php-ext-enable xdebug
+
+FROM base AS ci
+COPY composer.json composer.lock ./
+RUN composer install --prefer-dist --no-progress
+COPY . .

docker-compose.yaml

@@ -3,6 +3,7 @@ services:
         build:
             context: .
             dockerfile: ./config/docker/php/Dockerfile
+            target: dev
         volumes:
             - .:/app
         user: "33:33"