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/answer.js

@@ -0,0 +1,12 @@
+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);