Add PHP exif extension to prod Dockerfile for PWA image processing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/php/prod/Dockerfile

@@ -20,6 +20,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     zip \
     intl \
     gd \
+    exif \
     opcache \
     && pecl install redis imagick \
     && docker-php-ext-enable redis imagick \