存量积累：生图素人感约束+评图分+幂等防重跑+审核回路

- 015-017迁移：image_candidate 文案复审/AI视觉分/重生标记
- constants C7素人感约束(反电商摆拍对齐真实笔记)+C3叠字口子
- celery visibility_timeout=2h 防长任务被误判重投重复烧钱(task75教训)
- image_scorer 评图分(只筛选+展示,真实信号才进飞轮权重)
- storyboard/image_gen/pipeline_io 生图存量
- task_actions/tasks/task_service/flywheel 审核回路+飞轮存量

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/services/ai_engine/storyboard.py

@@ -9,7 +9,7 @@ storyboard 分镜引擎
 from __future__ import annotations
 import re
 from .constants import (
-    PAGE_ROLE_MAP, IMAGE_NEGATIVE_CONSTRAINTS,
+    PAGE_ROLE_MAP, IMAGE_NEGATIVE_CONSTRAINTS, IMAGE_XHS_STYLE_CONSTRAINTS,
     STYLE_PROMPTS, STYLE_DEFAULT, NARRATIVE_BY_COUNT, NARRATIVE_BY_STRATEGY,
 )
 # sanitize_text 移至 templates（腾行数），此处 re-export 供 image_gen 沿用 import
@@ -187,6 +187,7 @@ def plan_image_set(note: dict, product: dict, image_count: int = 3, analysis: di
         "禁止肤色变白、瑕疵消失、治疗前后等视觉暗示，允许安全的未推开/推开后质地状态对比；"
         "如果提供产品图，产品是不可修改的真实商品锚点，禁止改名、换包装、混入其他产品。"
         f"\n{IMAGE_NEGATIVE_CONSTRAINTS}"
+        f"\n{IMAGE_XHS_STYLE_CONSTRAINTS}"
     )
 
     return {