test(review): 新增 pytest 离线回归网，锁定 dwg_review 既有行为

在改动审查流水线（确定性检查前置 / 结论结构化 / 证据交叉校验）之前，
先立一张离线、确定性、秒级的回归网。

- tests/fakes.py：假 LLM + 假 MCP 基座 + 响应构造器（ok_text/ok_image/err）
  + make_ctx/make_evidence，绝不触网、不读密钥
- 10 个模块共 134 用例：
  mcp_client / llm_client / cad_tools / checklist / config /
  planning / evidence / review / report / annotator
- pytest.ini（testpaths=tests）+ requirements-dev.txt + 根 conftest.py
  （sys.path + RENDER_WAIT=0 / REPORT_DIR=tmp fixture）

tests/test_config.py

@@ -0,0 +1,68 @@
+"""`dwg_review.config` 单元测试（只验证纯函数与常量类型，不依赖真实环境变量）。"""
+
+import os
+
+from dwg_review import config
+
+
+def test_resolve_path_relative_uses_project_root():
+    assert config._resolve_path("reports") == config.PROJECT_ROOT / "reports"
+
+
+def test_resolve_path_absolute_unchanged(tmp_path):
+    assert config._resolve_path(str(tmp_path)) == tmp_path
+
+
+def test_project_root_is_repo_root():
+    assert (config.PROJECT_ROOT / "dwg_review" / "config.py").is_file()
+
+
+def test_read_env_prefers_environ(monkeypatch):
+    monkeypatch.setenv("CAD_TEST_ENV_PROBE", "hello")
+    assert config._read_env("CAD_TEST_ENV_PROBE") == "hello"
+
+
+def test_read_env_missing_returns_empty(monkeypatch):
+    monkeypatch.delenv("CAD_TEST_DEFINITELY_MISSING_XYZ", raising=False)
+    assert config._read_env("CAD_TEST_DEFINITELY_MISSING_XYZ") == ""
+
+
+def test_has_api_key_reflects_module_value(monkeypatch):
+    monkeypatch.setattr(config, "API_KEY", "")
+    assert config.has_api_key() is False
+    monkeypatch.setattr(config, "API_KEY", "sk-x")
+    assert config.has_api_key() is True
+
+
+def test_has_api_key_ignores_whitespace(monkeypatch):
+    monkeypatch.setattr(config, "API_KEY", "   ")
+    assert config.has_api_key() is False
+
+
+def test_constants_have_expected_types():
+    assert isinstance(config.HOST, str)
+    assert isinstance(config.PORT, int)
+    assert isinstance(config.CALL_TIMEOUT, float)
+    assert isinstance(config.CALL_RETRIES, int)
+    assert isinstance(config.MAX_FRAME_BYTES, int)
+    assert isinstance(config.IMAGE_MAX_EDGE, int)
+    assert isinstance(config.IMAGE_FORMAT, str)
+    assert isinstance(config.CHECKLIST_PATH, type(config.PROJECT_ROOT))
+
+
+def test_checklist_path_resolves_relative_to_root():
+    assert config.CHECKLIST_PATH.name == "review_checklist.json"
+    assert config.CHECKLIST_PATH.parent == config.PROJECT_ROOT
+
+
+def test_port_default_matches_baseline():
+    # 基座固定监听 127.0.0.1:8080；若此值被改动，请同步更新基座与文档。
+    assert config.HOST == "127.0.0.1"
+    assert config.PORT == 8080
+
+
+def test_os_name_guard_in_read_env(monkeypatch):
+    # 非 Windows 平台不应触碰注册表
+    monkeypatch.setattr(os, "name", "posix")
+    monkeypatch.delenv("CAD_TEST_ENV_PROBE2", raising=False)
+    assert config._read_env("CAD_TEST_ENV_PROBE2") == ""