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/answer.js

@@ -0,0 +1,40 @@
+const student = {
+  name: "林晨",
+  stage: "JavaScript 核心",
+};
+
+const scores = [78, 85, 92];
+
+function getAverageScore(list) {
+  let total = 0;
+
+  for (let index = 0; index < list.length; index += 1) {
+    total += list[index];
+  }
+
+  return total / list.length;
+}
+
+function getLevel(average) {
+  if (average >= 85) {
+    return "优秀";
+  }
+
+  if (average >= 70) {
+    return "良好";
+  }
+
+  return "继续努力";
+}
+
+const average = getAverageScore(scores);
+const level = getLevel(average);
+
+console.log("姓名：", student.name);
+console.log("阶段：", student.stage);
+console.log("平均分：", average);
+console.log("等级：", level);
+
+if (average >= 80) {
+  console.log("可以进入下一阶段");
+}