fix: 添加 audio_synthesis 表审核字段迁移

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/migrations/057_add_review_columns_to_audio_synthesis.sql

@@ -0,0 +1,8 @@
+-- 057: 为 audio_synthesis 表添加审核相关字段
+-- 对应 model: audio.py 中 AudioSynthesis 的 review_status 等字段
+
+ALTER TABLE aigcspace.audio_synthesis
+ADD COLUMN IF NOT EXISTS review_status VARCHAR(20) DEFAULT 'pending',
+ADD COLUMN IF NOT EXISTS reviewed_by INTEGER,
+ADD COLUMN IF NOT EXISTS reviewed_at TIMESTAMP,
+ADD COLUMN IF NOT EXISTS reject_reason VARCHAR(500);