feat(cps): 淘宝活动落地页图做活——每活动关联图,运营上传/选已有

- model: cps_activity.image_url + 迁移 cps_activity_image 回填存量淘宝活动为现有图
- admin: 新建淘宝活动必传图(上传 /upload-image 或选已有 /activity-images),存绝对 URL
- 落地页 cps_redirect: 按 link→activity 取图展示,缺图兜底默认图,img src 经 html.escape
- media: save_cps_image + to_abs_media_url(基于 CPS_REDIRECT_BASE,跨域 admin-web 可显示)

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

app/models/cps_activity.py

@@ -26,6 +26,8 @@ class CpsActivity(Base):
     product_view_sign: Mapped[str | None] = mapped_column(String(128), nullable=True)
     # 淘宝:整段淘口令文本(落地页原样复制);京东:推广链接(落地页 302 跳)。美团不用这个(用 act_id)。
     payload: Mapped[str | None] = mapped_column(Text, nullable=True)
+    # 淘宝落地页主视觉图(绝对 URL,基于 CPS_REDIRECT_BASE)。运营建活动时上传/选已有,落地页按活动展示。
+    image_url: Mapped[str | None] = mapped_column(String(512), nullable=True)
     status: Mapped[str] = mapped_column(String(20), nullable=False, default="active")  # active | archived
     remark: Mapped[str | None] = mapped_column(String(256), nullable=True)
     created_at: Mapped[datetime] = mapped_column(