docs: ui-signoff.ts 提示文案仍写死 R1-R8,requirements模板已升级到R1-R12(#819遗留)

`.harness/scripts/lib/ui-signoff.ts:47` 的提示文案还写着"写清楚这块 UI 背后的需求(R1-R8)",但 #819 已经把 `requirements.template.md` 从 R1-R8 升级到 R1-R12(Use Case格式)。requirement-author skill 的引用已同步,唯独这条给人看的引导文案漏了。

不影响功能(只是提示字符串),但会误导做UI signoff的人。建议顺手改成"R1-R12"或点出关键几节(如R3主流程/R4备选异常/R5权限)。

优先级:低,非阻断。

Open .harness/scripts/lib/ui-signoff.ts at line 47 and compare its user-facing prompt with requirements.template.md and the updated requirement-author skill reference. Update the stale R1-R8 wording to match the R1-R12 Use Case template, then verify the signoff prompt no longer mentions R1-R8.

Written by the indexing model from the issue text.