feat: add Docker setup exposing app on port 7876

- Dockerfile: php:apache base, installs PHP extensions + Composer,
  configures Apache to listen on port 7876, bundles app code,
  runs composer install at build time
- docker-compose.yml: web service (port 7876) + MariaDB LTS with
  healthcheck; writable volume for DB persistence
- docker/entrypoint.sh: generates .env from environment variables
  at container start, fixes runtime permissions
- docker/php.ini: tuned PHP limits (512M memory, 32M upload)
- .dockerignore: excludes .git, vendor, logs, cache, old docker dir
- .env.example: template for required environment variables

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,52 @@
+FROM php:apache
+
+# Build-time deps for PHP extensions
+RUN apt-get update && apt-get install -y --no-install-recommends \
+      libicu-dev libzip-dev libpng-dev libjpeg62-turbo-dev libfreetype6-dev \
+      libxml2-dev libcurl4-openssl-dev libonig-dev pkg-config unzip git tzdata \
+    && docker-php-ext-configure gd --with-jpeg --with-freetype \
+    && docker-php-ext-install -j"$(nproc)" \
+         pdo pdo_mysql mysqli intl zip gd bcmath mbstring curl xml \
+    && a2enmod rewrite headers \
+    && rm -rf /var/lib/apt/lists/*
+
+# Composer from official image
+COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
+
+# Configure Apache to listen on port 7876
+RUN sed -i 's/Listen 80/Listen 7876/' /etc/apache2/ports.conf \
+    && sed -i 's/<VirtualHost \*:80>/<VirtualHost *:7876>/' /etc/apache2/sites-available/000-default.conf
+
+# Set Apache DocumentRoot to /var/www/html/public
+RUN sed -ri -e 's!/var/www/html!/var/www/html/public!g' /etc/apache2/sites-available/000-default.conf
+
+# Apache request timeout
+RUN echo "Timeout 300" > /etc/apache2/conf-available/timeouts.conf && a2enconf timeouts
+
+# PHP config
+COPY docker/php.ini /usr/local/etc/php/conf.d/custom.ini
+
+WORKDIR /var/www/html
+
+# Copy application source
+COPY . .
+
+# Install Composer dependencies
+RUN composer install --no-interaction --prefer-dist --no-dev --optimize-autoloader
+
+# Base permissions: code owned root:www-data, writable dirs owned www-data
+RUN chown -R root:www-data /var/www/html \
+    && find /var/www/html -type d -exec chmod 755 {} \; \
+    && find /var/www/html -type f -exec chmod 644 {} \; \
+    && mkdir -p logs cache public/assets/uploads/avatars \
+    && chown -R www-data:www-data logs cache public/assets/uploads \
+    && chmod -R 775 logs cache public/assets/uploads \
+    && chmod 775 /var/www/html
+
+COPY docker/entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+
+EXPOSE 7876
+
+ENTRYPOINT ["/entrypoint.sh"]
+CMD ["apache2-foreground"]