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/08-built-in-methods/README.md

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+# 练习 8：常见内置方法
+
+## 目标
+
+学会使用几个常见的字符串和数组方法，减少重复代码。
+
+## 你要练什么
+
+- `trim()`
+- `toUpperCase()`
+- `includes()`
+- `join()`
+
+## 任务
+
+请完成一个“标签清洗器”脚本，要求：
+
+- 把一段带空格的文本去掉首尾空格
+- 把结果转成大写
+- 判断里面是否包含 `JS`
+- 把一个标签数组拼成一个字符串输出
+
+## 文件
+
+- [starter.js](/Users/lijiaqing/home/wwwroot/front-end-example/03-javascript-core/08-built-in-methods/starter.js)
+- [answer.js](/Users/lijiaqing/home/wwwroot/front-end-example/03-javascript-core/08-built-in-methods/answer.js)

03-javascript-core/08-built-in-methods/answer.js

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+const rawTitle = "  js 核心练习  ";
+const tags = ["变量", "条件", "函数"];
+
+const cleanTitle = rawTitle.trim();
+const upperTitle = cleanTitle.toUpperCase();
+const hasJS = upperTitle.includes("JS");
+const tagLine = tags.join("、");
+
+console.log("清洗后标题：", cleanTitle);
+console.log("大写标题：", upperTitle);
+console.log("是否包含 JS：", hasJS);
+console.log("标签列表：", tagLine);

03-javascript-core/08-built-in-methods/starter.js

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+const rawTitle = "  js 核心练习  ";
+const tags = ["变量", "条件", "函数"];
+
+// 任务：
+// 1. 去掉 rawTitle 两端空格
+// 2. 转成大写
+// 3. 判断是否包含 JS
+// 4. 把 tags 用顿号连接成一句话