feat(idx) finish idx system

backend/post.sql

@@ -7,6 +7,8 @@ CREATE TABLE IF NOT EXISTS Post
     last_update TIMESTAMP
 );
 
+drop table if exists post;
+
 INSERT INTO Post (post_id, title, summary, content, last_update)
 VALUES ($1, $2, $3, $4, $5)
 ON CONFLICT (post_id)