feat(调试): swapHair webui步数暴露到测试页可调

参数透传链路: 测试页→debug接口→generate_hairline_redraw→_grow_core
  →_call_swap→change_hair swapHair→webui_img2img→build_body_v2

- app.py: 调试接口新增 webui_steps Form 参数
- hairline_grow.py: _call_swap/_grow_core/generate_hairline_grow/generate_hairline_redraw 透传 webui_steps
- debug_grow_timing.html: 新增 swap步数 下拉(默认/10/15/20/25/30)

实测 steps 10→25 swap 耗时 4.1s→4.4s,参数确实生效

app.py

@@ -827,6 +827,7 @@ async def debug_grow_timing(
     image_url: Optional[str] = Form(default=None),
     image_base64: Optional[str] = Form(default=None),
     hair_style: str = Form(default="2", description="发型序号(花瓣=2)，逗号分隔多选"),
+    webui_steps: Optional[int] = Form(default=None, description="swapHair webui img2img 采样步数，None=服务端默认(15)，可填10/15/20/25对比"),
 ):
     """单图跑接口2女性生发，返回每个步骤的耗时 + 结果图，用于定位性能瓶颈。
 
@@ -903,7 +904,7 @@ async def debug_grow_timing(
                 t0 = _time.perf_counter()
                 data = await run_in_threadpool(
                     generate_hairline_redraw, redraw_img, chang_id,
-                    hair_mask=hair_mask_redraw, **_V2_FINAL_DEFAULTS)
+                    hair_mask=hair_mask_redraw, webui_steps=webui_steps, **_V2_FINAL_DEFAULTS)
                 t_redraw_pipeline = _time.perf_counter() - t0
                 _tm = data.get("timings_ms") or {}
                 entry["mask_ms"] = _tm.get("mask", 0)