docs(guide): add new appendix sections for product thinking

add four new appendix sections covering idea sources, double diamond model, jobs to be done, and mom test interview method. includes both zh-cn and en versions with comprehensive content and navigation updates.

update introduction.md and stage-0 index files to include new sections in tables of contents. add sidebar navigation entries in config.mjs for all languages.

each new appendix provides beginner-friendly explanations, practical frameworks, and AI integration tips for product development and validation.

docs/.vitepress/config.mjs

@@ -385,6 +385,24 @@ const productManagerSidebarEn = [
       }
     ]
   },
+  {
+    text: 'Appendix: User Research and Validation',
+    collapsed: false,
+    items: [
+      {
+        text: 'Jobs to Be Done',
+        link: '/en/stage-1/appendix-jobs-to-be-done/'
+      },
+      {
+        text: 'The Mom Test',
+        link: '/en/stage-1/appendix-mom-test/'
+      },
+      {
+        text: 'Double Diamond',
+        link: '/en/stage-1/appendix-double-diamond/'
+      }
+    ]
+  },
   {
     text: 'Appendix: Technical Solutions',
     collapsed: false,
@@ -1174,6 +1192,28 @@ const productManagerSidebar = [
       }
     ]
   },
+  {
+    text: '附录：用户研究与需求验证',
+    collapsed: false,
+    items: [
+      {
+        text: '从哪里找点子：3 种最适合新手的参考来源',
+        link: '/zh-cn/stage-1/appendix-idea-sources/'
+      },
+      {
+        text: '双钻模型：先做对的事，再把事做对',
+        link: '/zh-cn/stage-1/appendix-double-diamond/'
+      },
+      {
+        text: '用 Jobs to Be Done 找到用户真正想完成的事',
+        link: '/zh-cn/stage-1/appendix-jobs-to-be-done/'
+      },
+      {
+        text: 'The Mom Test 用户访谈法',
+        link: '/zh-cn/stage-1/appendix-mom-test/'
+      }
+    ]
+  },
   {
     text: '附录：技术方案',
     collapsed: false,