Add a lightweight schema migration runner, fix missing PHPMailer in prod image

docker-entrypoint-initdb.d only applies db/init.sql, and only on a brand new
volume - existing installs never got db/migrations/*.sql applied unless
someone ran them by hand. This bit twice this session (qr-oss's own init.sql
was missing a migration, and qr-vip's live DB was two migrations behind after
a code deploy). scripts/migrate.php now runs automatically on every container
start via a new entrypoint wrapper, applying any not-yet-recorded migration -
safe to run repeatedly since every migration file already checks
information_schema before altering.

Also caught in the process: Dockerfile.fpm (the production image) never
installed phpmailer/phpmailer, unlike the dev Dockerfile - meaning
self-registration's password email has been silently fatal-erroring in
production since the nginx+php-fpm switch.

Dockerfile.fpm

@@ -51,7 +51,9 @@ RUN cp -R ./php-qrcode/src /var/www/html/
 
 WORKDIR /var/www/html
 RUN composer update
+RUN composer require phpmailer/phpmailer:^6.9
 COPY ./src ./
+COPY ./db/migrations ./db/migrations
 RUN chown -R www-data:www-data /var/www/html \
     && find /var/www/html -type f -exec chmod 644 {} \; \
     && find /var/www/html -type d -exec chmod 755 {} \;
@@ -62,5 +64,13 @@ RUN mkdir -p /var/www/qrcode-storage/zip \
     && chown -R www-data:www-data /var/www/qrcode-storage \
     && chmod -R 775 /var/www/qrcode-storage
 
+# Applies any not-yet-applied db/migrations/*.sql on every container start (see
+# src/scripts/migrate.php) - docker-entrypoint-initdb.d only runs db/init.sql, and only
+# on a brand new volume, so without this an existing install's schema silently falls
+# behind the code on every `git pull` + restart.
+COPY docker/entrypoint.sh /usr/local/bin/entrypoint.sh
+RUN chmod +x /usr/local/bin/entrypoint.sh
+ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]
+
 EXPOSE 9000
 CMD ["php-fpm"]