Forum integration: Flarum extension, local test stack, embedded comments

- forum/extension: oc:import command (archived comments -> one thread per
  machine) and embed styling
- forum/docker: local Flarum 2 test stack
- site: optional params.forum.url adds a Forum menu entry and shows the
  machine thread in the Comments tab

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YDRjtmAiNpo5mK5N3d7QwZ

forum/docker/Dockerfile

@@ -0,0 +1,19 @@
+# Local test forum: Flarum 2 on Apache. Not the production install (see forum/README.md).
+FROM php:8.3-apache
+RUN apt-get update && apt-get install -y --no-install-recommends git unzip libzip-dev libpng-dev libjpeg-dev libfreetype6-dev \
+    && docker-php-ext-configure gd --with-jpeg --with-freetype \
+    && docker-php-ext-install pdo_mysql gd zip \
+    && a2enmod rewrite && rm -rf /var/lib/apt/lists/*
+COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
+ENV COMPOSER_ALLOW_SUPERUSER=1
+RUN composer create-project flarum/flarum /var/www/flarum "^2.0" --no-interaction --prefer-dist \
+    && cd /var/www/flarum && mkdir packages \
+    && composer require --no-interaction flarum/embed "^2.0" \
+    && composer config repositories.oc '{"type": "path", "url": "packages/*", "options": {"symlink": true}}' \
+    && chown -R www-data:www-data /var/www/flarum
+RUN sed -ri 's#/var/www/html#/var/www/flarum/public#g' /etc/apache2/sites-available/000-default.conf \
+    && printf '<Directory /var/www/flarum/public>\n  AllowOverride All\n  Require all granted\n</Directory>\n' > /etc/apache2/conf-enabled/flarum.conf
+COPY entrypoint.sh /entrypoint.sh
+WORKDIR /var/www/flarum
+ENTRYPOINT ["/entrypoint.sh"]
+CMD ["apache2-foreground"]