글쓰기 태그 제한과 표 기능 추가

Co-authored-by: Cursor <cursoragent@cursor.com>

db/migrations/056_site_settings_post_tag_limit.sql

@@ -0,0 +1,10 @@
+ALTER TABLE site_settings
+  ADD COLUMN IF NOT EXISTS post_tag_limit INTEGER NOT NULL DEFAULT 5;
+
+ALTER TABLE site_settings
+  ADD CONSTRAINT site_settings_post_tag_limit_range_check
+  CHECK (post_tag_limit BETWEEN 1 AND 10)
+  NOT VALID;
+
+ALTER TABLE site_settings
+  VALIDATE CONSTRAINT site_settings_post_tag_limit_range_check;