docs: prd 폴더와 sample-prd 추가, 기존 계획 문서 plan-task 폴더 아래로 이동

docs/plan-task/20260407_audio_content_settlement_ratio_ddl.sql

@@ -0,0 +1,19 @@
+SET @schema_name := DATABASE();
+
+SET @settlement_ratio_column_exists := (
+    SELECT COUNT(1)
+    FROM information_schema.columns
+    WHERE table_schema = @schema_name
+      AND table_name = 'content'
+      AND column_name = 'settlement_ratio'
+);
+
+SET @add_settlement_ratio_column_sql := IF(
+    @settlement_ratio_column_exists = 0,
+    'ALTER TABLE content ADD COLUMN settlement_ratio INT NULL COMMENT ''콘텐츠별 정산 요율(%)'' AFTER price',
+    'SELECT ''content.settlement_ratio already exists'' AS message'
+);
+
+PREPARE add_settlement_ratio_column_stmt FROM @add_settlement_ratio_column_sql;
+EXECUTE add_settlement_ratio_column_stmt;
+DEALLOCATE PREPARE add_settlement_ratio_column_stmt;