feat: implement wiki and submission management services with corresponding database schema and API endpoints

db/migrations/000016_wiki_content.up.sql

@@ -3,6 +3,7 @@ CREATE TABLE IF NOT EXISTS wiki_content (
     wiki_id UUID NOT NULL REFERENCES wikis(id) ON DELETE CASCADE,
     title TEXT NOT NULL,
     content TEXT,
+    preview TEXT,
     is_deleted BOOLEAN NOT NULL DEFAULT false,
     created_at TIMESTAMPTZ DEFAULT now()
 );