test: 接入覆盖率工具并在 CI 强制 ≥80% 门禁

后端: 加 pytest-cov + [tool.coverage] 配置, pytest --cov-fail-under=80 (基线~88%)。
前端: 加 @vitest/coverage-v8, vitest.config.ts 设 80% 阈值, 新增 test:coverage 脚本 (基线~93%)。
前端覆盖范围限定 lib/** 纯逻辑层; hooks(use*.ts)待 jsdom 测试栈接入后纳入。
CI backend/frontend job 改跑覆盖率门禁命令。CLAUDE.md 同步 DoD 与 Toolchain。

pyproject.toml

@@ -14,6 +14,7 @@ members = [
 dev = [
   "pytest>=8",
   "pytest-asyncio>=0.24",
+  "pytest-cov>=5",
   "ruff>=0.6",
   "mypy>=1.11",
   "httpx>=0.27",
@@ -51,3 +52,23 @@ exclude = ["(^|/)conftest\\.py$"]
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 testpaths = ["tests", "apps", "packages"]
+
+[tool.coverage.run]
+branch = true
+source = ["apps", "packages"]
+omit = [
+  "*/tests/*",
+  "*/conftest.py",
+  "*/migrations/*",
+  "*/alembic/*",
+]
+
+[tool.coverage.report]
+show_missing = true
+# 排除无需覆盖的纯防御/类型分支
+exclude_lines = [
+  "pragma: no cover",
+  "raise NotImplementedError",
+  "if TYPE_CHECKING:",
+  "@(abc\\.)?abstractmethod",
+]