feat(C-03)：代码在线运行+课程练一节

新增CodeRunner组件（JS worker沙箱+Python pyodide）与/utility/code-runner独立页；CourseLearn新增练习Tab（首代码块自动提取装载，无示例可直接练习）。

src/components/CodeRunner/pyodide-runner.ts

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+/**
+ * C-03 Pyodide 懒加载运行器（浏览器内 WASM，无服务端执行）。
+ * 安全约束：
+ * - 默认断网：不 loadPackage、不拉取额外包；只运行解释器自带能力。
+ * - 超时由调用方（CodeRunner.tsx）经 Promise.race + runId 丢弃过期结果保证；
+ *   Pyodide 本体不支持强制 terminate，超时后输出"执行超时"并忽略迟到结果。
+ */
+
+export const PYODIDE_VERSION = "0.26.4";
+export const PYODIDE_CDN = `https://cdn.jsdelivr.net/pyodide/v${PYODIDE_VERSION}/full/`;
+
+type PyodideRuntime = {
+  runPython: (code: string) => unknown;
+  setStdout: (opts: { batched: (s: string) => void }) => void;
+  setStderr: (opts: { batched: (s: string) => void }) => void;
+};
+
+declare global {
+  interface Window {
+    __pyodidePromise?: Promise<PyodideRuntime> | null;
+  }
+}
+
+function loadPyodideScript(): Promise<void> {
+  return new Promise((resolve, reject) => {
+    if (document.querySelector('script[data-pyodide="1"]')) {
+      resolve();
+      return;
+    }
+    const s = document.createElement("script");
+    s.dataset.pyodide = "1";
+    s.src = `${PYODIDE_CDN}pyodide.js`;
+    s.onload = () => resolve();
+    s.onerror = () => reject(new Error("Pyodide 运行时加载失败，请检查网络后重试"));
+    document.head.appendChild(s);
+  });
+}
+
+async function bootPyodide(
+  onStdout: (s: string) => void,
+  onStderr: (s: string) => void,
+): Promise<PyodideRuntime> {
+  await loadPyodideScript();
+  const factory = (window as unknown as { loadPyodide?: (opts: { indexURL: string }) => Promise<PyodideRuntime> }).loadPyodide;
+  if (!factory) throw new Error("Pyodide 运行时初始化失败");
+  const py = await factory({ indexURL: PYODIDE_CDN });
+  py.setStdout({ batched: onStdout });
+  py.setStderr({ batched: onStderr });
+  return py;
+}
+
+export function getPyodide(
+  onStdout: (s: string) => void,
+  onStderr: (s: string) => void,
+): Promise<PyodideRuntime> {
+  if (!window.__pyodidePromise) {
+    window.__pyodidePromise = bootPyodide(onStdout, onStderr).catch((e) => {
+      window.__pyodidePromise = null;
+      throw e;
+    });
+  }
+  return window.__pyodidePromise;
+}