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

static/debug_grow_timing.html

@@ -80,6 +80,17 @@
           <option value="5">5 波浪</option>
         </select>
       </div>
+      <div class="form-group">
+        <label>swap步数</label>
+        <select id="webuiSteps">
+          <option value="">默认(15)</option>
+          <option value="10">10 (最快)</option>
+          <option value="15">15</option>
+          <option value="20">20 (原版)</option>
+          <option value="25">25 (高画质)</option>
+          <option value="30">30</option>
+        </select>
+      </div>
       <button class="btn btn-primary" id="submitBtn" onclick="submitTest()">🚀 开始分析</button>
     </div>
     <div id="statusBar" class="status hidden"></div>
@@ -115,6 +126,8 @@ async function submitTest(){
   const fd = new FormData();
   fd.append('image_file', f);
   fd.append('hair_style', $('hairStyle').value);
+  const _steps = $('webuiSteps').value;
+  if(_steps !== '') fd.append('webui_steps', _steps);
 
   try{
     const r = await fetch(API_BASE+'/api/v1/debug/grow-timing',{