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/07-objects/starter.js

@@ -0,0 +1,11 @@
+const course = {
+  title: "JavaScript 核心",
+  lessons: 12,
+  finished: false,
+};
+
+// 任务：
+// 1. 修改 finished
+// 2. 新增 teacher 属性
+// 3. 输出完整对象
+// 4. 输出 title 和 teacher