docs: update project practice duration and refine final assignment

- Increase estimated duration from "about 1 day" to "about 3 days"
- Remove path options and reframe assignment as open-ended project
- Update requirements to emphasize industry scenario selection and comprehensive skill application
- Simplify checklist and clarify deliverables (prototype + 30-second demo video)

docs/.vitepress/config.mjs

@@ -289,10 +289,6 @@ export default defineConfig({
               text: '4. 完整项目实战',
               link: '/zh-cn/stage-1/1.4-complete-project-practice/'
             },
-            {
-              text: '5. 大作业：完成一个 Web 应用原型',
-              link: '/zh-cn/stage-1/1.5-final-project/'
-            },
             {
               text: '附录 A：产品思维补充',
               link: '/zh-cn/stage-1/appendix-a-product-thinking/'
@@ -301,6 +297,10 @@ export default defineConfig({
               text: '附录 B：常见报错及解决方案',
               link: '/zh-cn/stage-1/appendix-b-common-errors/'
             },
+            {
+              text: '附录 C：产业多分类场景方向参考',
+              link: '/zh-cn/stage-1/appendix-industry-scenarios/'
+            },
             {
               text: '扩展阅读 1：7 款主流 Vibe Coding 在线平台实测对比',
               link: '/zh-cn/stage-1/appendix-articles/example0-1/vibe-coding-tools-snake-game-tutorial'