feat: Add JavaScript core exercises and solutions

- Implemented exercises for array high-order methods, memory and execution, switch statements, and final review.
- Added starter and answer files for each exercise to facilitate learning.
- Created a runner HTML file to execute JavaScript code and display console outputs.
- Updated README files to include exercise objectives, tasks, and usage instructions.

03-javascript-core/06-arrays/README.md

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+# 练习 6：数组
+
+## 目标
+
+学会保存一组同类数据，并对数组做基础读写。
+
+## 你要练什么
+
+- 数组声明
+- 下标访问
+- `length`
+- `push()`
+- 遍历数组
+
+## 任务
+
+请完成一个“学习清单”脚本，要求：
+
+- 创建一个包含 3 个学习主题的数组
+- 新增 1 个学习主题
+- 输出数组长度
+- 依次输出每个学习主题
+
+## 文件
+
+- [starter.js](/Users/lijiaqing/home/wwwroot/front-end-example/03-javascript-core/06-arrays/starter.js)
+- [answer.js](/Users/lijiaqing/home/wwwroot/front-end-example/03-javascript-core/06-arrays/answer.js)