Fix RLS policy: allow publishing by adding 'published' to WITH CHECK

The WITH CHECK clause was missing 'published', causing publish action
to be blocked by row-level security.

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

Author: Yushin-L

supabase/migrations/006_post_drafts_soft_delete.sql

@@ -25,5 +25,5 @@ CREATE POLICY "Authors can update own drafts"
   )
   WITH CHECK (
     author_id = auth.uid()
-    AND status IN ('draft', 'pending', 'deleted')
+    AND status IN ('draft', 'pending', 'published', 'deleted')
   );