Adds Docker support for TravianZ

Introduces Docker Compose configuration for simplified deployment.

Includes a Dockerfile to build the application image and necessary configurations for running TravianZ in a containerized environment.

Provides documentation for setup and usage in `DOCKER_README.md`.

Dockerfile

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+FROM php:7.4-apache
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y \
+    libpng-dev \
+    libjpeg-dev \
+    libfreetype6-dev \
+    libzip-dev \
+    zip \
+    unzip \
+    git \
+    && rm -rf /var/lib/apt/lists/*
+
+# Configure and install PHP extensions
+RUN docker-php-ext-configure gd --with-freetype --with-jpeg \
+    && docker-php-ext-install -j$(nproc) \
+    gd \
+    mysqli \
+    pdo \
+    pdo_mysql \
+    zip
+
+# Enable Apache modules
+RUN a2enmod rewrite headers
+
+# Set working directory
+WORKDIR /var/www/html
+
+# Copy application files
+COPY . /var/www/html/
+
+# Set permissions
+RUN chown -R www-data:www-data /var/www/html \
+    && chmod -R 755 /var/www/html \
+    && chmod -R 777 /var/www/html/var
+
+# Configure Apache to use /var/www/html as DocumentRoot
+RUN sed -i 's!/var/www/html!/var/www/html!g' /etc/apache2/sites-available/000-default.conf
+
+# Expose port 80
+EXPOSE 80
+
+# Start Apache
+CMD ["apache2-foreground"]