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/entrypoint.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+# First start: install Flarum against the db service, enable the extensions the site relies on.
+set -e
+cd /var/www/flarum
+if [ ! -f config.php ]; then
+  until php -r 'new PDO("mysql:host=db;dbname=flarum", "flarum", "flarum");' >/dev/null 2>&1; do sleep 2; done
+  cat > /tmp/install.yml <<Y
+debug: true
+baseUrl: ${FORUM_URL}
+databaseConfiguration:
+  driver: mysql
+  host: db
+  port: 3306
+  database: flarum
+  username: flarum
+  password: flarum
+  prefix:
+adminUser:
+  username: admin
+  password: ${ADMIN_PASSWORD}
+  email: admin@example.com
+settings:
+  forum_title: Old-Computers.com forum
+Y
+  php flarum install --file=/tmp/install.yml
+fi
+# the museum extension is mounted from the repository (forum/extension)
+composer require --no-interaction "oc/flarum-museum:*@dev" >/dev/null 2>&1 || composer require --no-interaction "oc/flarum-museum:*@dev"
+php flarum migrate
+for ext in flarum-tags flarum-markdown flarum-embed oc-museum; do php flarum extension:enable "$ext" || true; done
+php flarum cache:clear
+chown -R www-data:www-data storage public/assets
+exec docker-php-entrypoint "$@"