feat(backend): 重构 HTTP 错误处理为 RFC7807 标准并优化多个 service

backend/tests/unit/test_response_envelope.py

@@ -12,6 +12,8 @@ def test_problem_details_defaults() -> None:
     assert result.status == 401
     assert result.detail == "Unauthorized"
     assert result.instance is None
+    assert result.code is None
+    assert result.params is None
 
 
 def test_problem_details_overrides() -> None:
@@ -21,6 +23,8 @@ def test_problem_details_overrides() -> None:
         type_value="https://example.com/problems/conflict",
         title="Conflict",
         instance="/api/mobile/auth/signup",
+        code="AUTH_CONFLICT",
+        params={"field": "email"},
     )
 
     assert result.type == "https://example.com/problems/conflict"
@@ -28,3 +32,5 @@ def test_problem_details_overrides() -> None:
     assert result.status == 409
     assert result.detail == "Conflict"
     assert result.instance == "/api/mobile/auth/signup"
+    assert result.code == "AUTH_CONFLICT"
+    assert result.params == {"field": "email"}