build: simplify Dockerfile using extension installer

- Replace manual apk install and docker-php-ext-install with mlocati/docker-php-extension-installer
- Combine system dependency installation and PHP extension setup into a single step
- Reorder steps for better clarity: copy files before permission fixes
- Maintain same PHP extensions and final permissions

Dockerfile

@@ -2,29 +2,22 @@ FROM php:8.4-fpm-alpine
 
 WORKDIR /var/www
 
-# Install system dependencies
-RUN apk add --no-cache \
-    git \
-    curl \
-    libpng-dev \
-    oniguruma-dev \
-    libxml2-dev \
-    zip \
-    unzip \
-    libzip-dev \
-    icu-dev
+# Install the PHP extension installer helper
+ADD https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
 
-# Install PHP extensions
-RUN docker-php-ext-install pdo_mysql mbstring exif pcntl bcmath gd zip intl
-
-# Clear cache
-RUN rm -rf /var/cache/apk/*
+# Install system dependencies and PHP extensions in one go
+# This script handles the 'apk add' and 'apk del' for dev-libraries automatically
+RUN chmod +x /usr/local/bin/install-php-extensions && \
+    install-php-extensions pdo_mysql mbstring exif pcntl bcmath gd zip intl
 
 # Get latest Composer
 COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
 
-# Copy application files and fix permissions
+# Copy application files
 COPY . /var/www
+
+# Fix permissions
+# We do this as root before switching to the unprivileged user
 RUN chown -R www-data:www-data /var/www && \
     find /var/www -type d -exec chmod 755 {} + && \
     find /var/www -type f -exec chmod 644 {} + && \