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/extension/extend.php

@@ -0,0 +1,11 @@
+<?php
+
+use Flarum\Extend;
+use Oc\Museum\Console\ImportCommand;
+
+return [
+    (new Extend\Console())->command(ImportCommand::class),
+
+    // threads shown inside the museum pages (flarum/embed) take the look of the static site
+    (new Extend\Frontend('embed'))->css(__DIR__.'/less/embed.less'),
+];