feat: jc 引擎主线搬入 app/engine（315 测试基线全绿：320 去掉 admin 5 用例）

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

tests/test_ip_service.py

@@ -0,0 +1,18 @@
+def test_resolve_region_code():
+    from app.engine.services.ip_service import resolve_region_code
+    # 公网IP返回 ISO alpha-2 或 None(查不到),绝不返回中文/"本地"/"未知"
+    r = resolve_region_code("104.28.41.169")
+    assert r is None or (isinstance(r, str) and len(r) == 2 and r.isupper() and r.isalpha())
+    assert resolve_region_code("") is None
+    assert resolve_region_code("127.0.0.1") is None
+    assert resolve_region_code("::1") is None
+
+def test_country_names_ca_bug_fixed():
+    from app.engine.services import ip_service
+    assert ip_service.COUNTRY_NAMES.get("CA") == "加拿大"
+    assert ip_service.COUNTRY_NAMES.get("AU") == "澳大利亚"
+
+
+def test_resolve_region_code_known_ip_deterministic():
+    from app.engine.services.ip_service import resolve_region_code
+    assert resolve_region_code("8.8.8.8") == "US"   # Google DNS, 离线库确定性