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/14-memory-and-execution/starter.js

@@ -0,0 +1,28 @@
+let scoreA = 80;
+let scoreB = scoreA;
+
+const userA = {
+  name: "小周",
+  city: "上海",
+};
+
+const userB = userA;
+
+function printStepOne() {
+  console.log("步骤一");
+}
+
+function printStepTwo() {
+  console.log("步骤二");
+}
+
+function updateUser(user) {
+  // 任务：
+  // 1. 修改 user.city
+}
+
+// 任务：
+// 2. 修改 scoreB，观察 scoreA 是否变化
+// 3. 修改 userB.city，观察 userA.city 是否变化
+// 4. 按顺序调用 printStepOne 和 printStepTwo
+// 5. 调用 updateUser(userA)