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/10-final-mini-app/starter.js

@@ -0,0 +1,20 @@
+const student = {
+  name: "林晨",
+  stage: "JavaScript 核心",
+};
+
+const scores = [78, 85, 92];
+
+function getAverageScore(list) {
+  // 计算平均分
+}
+
+function getLevel(average) {
+  // 返回等级
+}
+
+// 任务：
+// 1. 计算平均分
+// 2. 计算等级
+// 3. 输出姓名、阶段、平均分、等级
+// 4. 如果平均分 >= 80，输出“可以进入下一阶段”