refactor(接口3): 简化为只需划线图一张，去掉 original + best_hairline

按需求方意见——B端只需上传一张已画好发际线的图，用不着原图：
- 入参去掉 original_image_*，只保留 marked_image_*(三选一)
- 输出去掉 best_hairline_image_url，只返回 hair_growth_image_url + hairline_type
- ComfyUI 输入图改用 marked 划线图原样(add_hair.json 本就是"画了线的照片"，
  提示词清除黑线)；检测路径只用于建遮罩，不再重画干净线/不需对齐原图
- service.generate_grow_b 签名改 (marked_bgr) 单参
- 同步文档：接口文档/接口3技术方案/网关映射表(去掉接口3 best_hairline 行)
- 测试更新：grow-b 只传 marked，断言无 best_hairline 字段，44全绿

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

tests/test_api.py

@@ -106,33 +106,27 @@ def test_grow_female_returns_5(client, monkeypatch):
 GROWB = "/api/v1/hair/grow-b"
 
 
-def test_growb_missing_original_1007(client):
-    files = {"marked_image_file": ("m.jpg", open(fixture("marked_hairline.jpg"), "rb"), "application/octet-stream")}
-    r = client.post(GROWB, headers=H, files=files)
+def test_growb_missing_marked_1007(client):
+    r = client.post(GROWB, headers=H)                       # 一张图都没传
     assert r.json()["code"] == 1007
 
 
 def test_growb_no_line_1001(client):
-    f = lambda: open(fixture("frontal.jpg"), "rb")
-    files = {"marked_image_file": ("m.jpg", f(), "application/octet-stream"),
-             "original_image_file": ("o.jpg", f(), "application/octet-stream")}
-    r = client.post(GROWB, headers=H, files=files)
+    files = {"marked_image_file": ("m.jpg", open(fixture("frontal.jpg"), "rb"), "application/octet-stream")}
+    r = client.post(GROWB, headers=H, files=files)         # 无划线 → 拒识
     assert r.json()["code"] == 1001
 
 
 def test_growb_success(client, monkeypatch):
     import hairline.comfyui as comfy
     monkeypatch.setattr(comfy, "run", lambda *a, **k: _PNG_1x1)
-    fm = open(fixture("marked_hairline.jpg"), "rb")
-    fo = open(fixture("marked_hairline.jpg"), "rb")
-    files = {"marked_image_file": ("m.jpg", fm, "application/octet-stream"),
-             "original_image_file": ("o.jpg", fo, "application/octet-stream")}
-    body = client.post(GROWB, headers=H, files=files).json()
+    files = {"marked_image_file": ("m.jpg", open(fixture("marked_hairline.jpg"), "rb"), "application/octet-stream")}
+    body = client.post(GROWB, headers=H, files=files).json()  # 只传划线图一张
     assert body["code"] == 0, body
     d = body["data"]
     assert d["hairline_type"] == "custom"
     assert base64.b64decode(d["hair_growth_image_base64"])[:8] == b"\x89PNG\r\n\x1a\n"
-    assert d["best_hairline_image_base64"]                 # 原图原样(非空)
+    assert "best_hairline_image_base64" not in d            # 已去掉该字段
     assert "best_hairline_image_url" not in d