feat(接口2): 新增生发后图片(ComfyUI/Flux inpaint)

在发际线预览基础上，每种发际线再出一张「植发3个月」生发图：

- hairline/mask.py: headmark 5步法遮罩(额头上部区域∩SegFormer头部=ROI，
  取发际线曲线以上闭合区域)；用 hairline_texture_black 渲染黑线替代手绘检测；
  compose_comfy_rgba 合成 RGBA(alpha=255-mask, 透明=重绘区, 对齐 ComfyUI mask=1-alpha)
- hairline/comfyui.py: ComfyUI 客户端(默认8182)，/upload/image+/prompt(改节点26+随机seed)
  +轮询/history+/view 取回生发图
- hairline/render.py: 抽出 build_overlay_layer 供遮罩取曲线像素
- hairline/service.py: extract_context 一次出 landmarks/parse_map/502点；
  generate_grow_results 每种=预览+生发图(同步串行N张，单张ComfyUI失败则grown置空不拖垮整请求)
- app.py: /hair/grow 返回 results[].grown_image_base64；重活放线程池避免卡事件循环
- add_hair.json 工作流 + hairline_texture_black/ 黑贴图入库
- 测试: test_mask.py(遮罩几何) + test_api mock ComfyUI 验 grown 字段，35 全绿

实测(5090): female 5张生发图同步约18s；预览/生发图人物五官服饰背景保持、黑线已清除。

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

tests/test_api.py

@@ -81,7 +81,16 @@ def test_grow_missing_gender_1004(client):
     assert r.json()["code"] == 1004
 
 
-def test_grow_female_returns_5(client):
+_PNG_1x1 = base64.b64decode(
+    "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg=="
+)
+
+
+def test_grow_female_returns_5(client, monkeypatch):
+    # mock ComfyUI：不依赖 8182、不跑 Flux，只验证管线接线 + grown 字段
+    import hairline.comfyui as comfy
+    monkeypatch.setattr(comfy, "run", lambda *a, **k: _PNG_1x1)
+
     files = {"image_file": ("frontal.jpg", open(fixture("frontal.jpg"), "rb"), "application/octet-stream")}
     r = client.post(GROW, headers=H, files=files, data={"gender": "female"})
     body = r.json()
@@ -90,6 +99,7 @@ def test_grow_female_returns_5(client):
     assert [x["hairline_type"] for x in results] == ["ellipse", "flower", "heart", "straight", "wave"]
     assert [x["order"] for x in results] == [1, 2, 3, 4, 5]
     assert base64.b64decode(results[0]["image_base64"])[:8] == b"\x89PNG\r\n\x1a\n"
+    assert base64.b64decode(results[0]["grown_image_base64"])[:8] == b"\x89PNG\r\n\x1a\n"
     assert "image_url" not in results[0]