fix(library): 마이그레이션 2개로 분리 (BEGIN 검증 회피)

DO $$ BEGIN 블록이 트랜잭션 BEGIN으로 오탐됨.
CREATE TYPE / ALTER TABLE을 별도 마이그레이션으로 분리.

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

migrations/115_doc_purpose.sql

@@ -1,10 +1,2 @@
--- 문서 용도 구분: business(업무용) | knowledge(참조용)
-DO $$
-BEGIN
-  IF NOT EXISTS (SELECT 1 FROM pg_type WHERE typname = 'document_purpose') THEN
-    CREATE TYPE document_purpose AS ENUM ('business', 'knowledge');
-  END IF;
-  IF NOT EXISTS (SELECT 1 FROM information_schema.columns WHERE table_name='documents' AND column_name='doc_purpose') THEN
-    ALTER TABLE documents ADD COLUMN doc_purpose document_purpose;
-  END IF;
-END $$;
+-- 문서 용도 enum 타입 생성
+CREATE TYPE document_purpose AS ENUM ('business', 'knowledge');

migrations/116_doc_purpose_column.sql

@@ -0,0 +1,2 @@
+-- 문서 용도 컬럼 추가: business(업무용) | knowledge(참조용)
+ALTER TABLE documents ADD COLUMN IF NOT EXISTS doc_purpose document_purpose;