fix: 将52号接口范围限定为GPU worker

撤回52号网关路由、图片字段改名和mock改动，gateway目录恢复a3fddbb。worker保持base64和null响应，更新接口说明和回归测试。

验证：worker API、IP限制与网关兼容性共54项测试通过。

tests/test_gateway_hairline_routes.py

@@ -1,16 +1,12 @@
-"""The legacy interface 5 and new interface 52 forward to separate worker paths."""
+"""Interface 52 belongs to the GPU worker; the gateway keeps its legacy routes."""
 import asyncio
 import importlib
 
-import pytest
 from starlette.requests import Request
 
 
-@pytest.mark.parametrize("name,path", [
-    ("hairline_generate", "/api/v1/hairline/generate"),
-    ("hairline_generate_52", "/api/v1/hairline/generate-52"),
-])
-def test_distinct_hairline_forwarding(monkeypatch, name, path):
+def test_legacy_hairline_forwarding(monkeypatch):
+    name, path = "hairline_generate", "/api/v1/hairline/generate"
     gateway = importlib.import_module("gateway.app")
     request = Request({"type": "http", "method": "POST", "path": path, "headers": []})
     calls = []
@@ -25,3 +21,9 @@ def test_distinct_hairline_forwarding(monkeypatch, name, path):
     assert next(route for route in gateway.app.routes if getattr(route, "path", None) == path).endpoint is endpoint
     assert asyncio.run(endpoint(request)) == {"forwarded_to": path}
     assert calls == [path]
+
+
+def test_interface52_is_not_exposed_by_gateway():
+    gateway = importlib.import_module("gateway.app")
+    assert not any(getattr(route, "path", None) == "/api/v1/hairline/generate-52"
+                   for route in gateway.app.routes)