docs: add product requirements overview (#18)

tests/test_harness_docs.py

@@ -58,6 +58,17 @@ class CoreDocumentTests(unittest.TestCase):
         self.assertIn(path, CORE_DOCUMENT_REQUIREMENTS)
         self.assertIn("## 可复制 Agent 指令", CORE_DOCUMENT_REQUIREMENTS[path])
 
+    def test_product_requirements_overview_is_core_document(self) -> None:
+        path = "docs/09-product-requirements-overview.md"
+        self.assertEqual(
+            CORE_PAGE_PATHS.get("Product-Requirements-Overview"),
+            path,
+        )
+        required = CORE_DOCUMENT_REQUIREMENTS[path]
+        self.assertIn("## 当前需求索引", required)
+        self.assertIn("## 原型与设计资产", required)
+        self.assertIn("## 更新时机", required)
+
     def test_existing_project_adoption_requires_upgrade_process(self) -> None:
         required = CORE_DOCUMENT_REQUIREMENTS[
             "docs/08-existing-project-adoption.md"
@@ -77,6 +88,7 @@ class CoreDocumentTests(unittest.TestCase):
         self.assertIn("### 2. 选择建设基线", required)
         self.assertIn("#### 判断案例", required)
         self.assertIn("### 3. 识别子项目与交付单元", required)
+        self.assertIn("#### 需求总览启用条件", required)
 
     def test_missing_or_wrong_core_mapping_is_reported(self) -> None:
         errors = core_mapping_errors({"Home": "docs/wrong.md"})