feat: Initial commit for Saqel Platform architecture, backend, Docker, and documentation

docker/php/Dockerfile

@@ -0,0 +1,23 @@
+FROM php:8.3-fpm-alpine
+
+RUN apk add --no-cache nginx icu-dev libzip-dev zip oniguruma-dev libpng-dev freetype-dev libjpeg-turbo-dev \
+    && docker-php-ext-configure gd --with-freetype --with-jpeg \
+    && docker-php-ext-install pdo_mysql bcmath intl zip gd opcache pcntl
+
+COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
+
+WORKDIR /var/www
+
+COPY backend/composer.json backend/composer.lock ./
+RUN composer install --no-dev --no-scripts --no-autoloader --prefer-dist --no-interaction
+
+COPY backend .
+RUN composer dump-autoload --optimize \
+    && php artisan config:cache || true \
+    && php artisan route:cache || true
+
+RUN chown -R www-data:www-data storage bootstrap/cache
+
+EXPOSE 9000
+
+CMD ["php-fpm"]