feat: implement article version content storage and reconstruction logic; enhance article repository with version management

server/migrations/20260407100000_add_article_version_content_storage.down.sql

@@ -0,0 +1 @@
+SELECT 1;

server/migrations/20260407100000_add_article_version_content_storage.up.sql

@@ -0,0 +1,6 @@
+UPDATE articles
+SET current_version_id = NULL,
+    updated_at = NOW()
+WHERE current_version_id IS NOT NULL;
+
+DELETE FROM article_versions;