Set hasDiscussionBody flag on SMF1 source

SMF1's discussions() export joins smf_messages to embed the first
post body in the Discussion record, and comments() excludes it
(ID_MSG <> ID_FIRST_MSG). Without declaring hasDiscussionBody,
the base Package default (false) causes Controller::setFlags()
to skip OP extraction on both source and target. The result is
that first posts are silently lost during migration.

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

Author: 2 people

src/Source/Smf1.php

@@ -12,6 +12,10 @@
 
 class Smf1 extends Source
 {
+    protected const array FLAGS = [
+        'hasDiscussionBody' => true, // SMF stores the OP body in the discussion export.
+    ];
+
     public const SUPPORTED = [
         'name' => 'Simple Machines 1',
         'defaultTablePrefix' => 'smf_',