prompt-enhancement 2

Prompt enhancement for the dsh web GUI: rewrite the composer draft into a well-structured prompt through the harness LLM service, preview the before/after, then fill back, copy, or undo. Original draft is always preserved.

一键把输入框草稿改写为更清晰、更贴 Agent 执行的提示词：直接替换 + 一键撤回，带保真闸与长度闸。