perf: skulpt 改为按需加载，client-zip 换成 fflate

skulpt 此前被 SubmitCode.vue 静态引用，945K 的 chunk 落在做题页首屏，
学生打开任何一道题都要下 233KB gzip，只为提交时拿一个语法错误行号。
改成 import() 懒加载并在语言切到 Python3 时预取，加载失败放行提交、
交给后端判题兜底。构建产物确认该 chunk 只剩一处 import() 引用，
index.html 不再引用。

client-zip 的能力 fflate 已经覆盖（utils/functions.ts 本就在用 zlibSync），
新增 createZipBlob 统一两处测试用例打包，删掉该依赖。压缩方式由 store
变为 deflate，Python zipfile 透明解压，后端不受影响。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

package-lock.json

@@ -26,7 +26,6 @@
         "canvas-confetti": "^1.9.4",
         "chart.js": "^4.5.1",
         "chartjs-chart-wordcloud": "^4.4.5",
-        "client-zip": "^2.5.0",
         "codemirror": "^6.0.2",
         "copy-text-to-clipboard": "^3.2.2",
         "date-fns": "^4.4.0",
@@ -2116,6 +2115,29 @@
         "vue": "^3.0.11"
       }
     },
+    "node_modules/@emnapi/core": {
+      "version": "1.11.3",
+      "resolved": "https://registry.npmjs.org/@emnapi/core/-/core-1.11.3.tgz",
+      "integrity": "sha512-zLpS5asjEb7lq8jYLq37N6XKaE41DIexlY1rF/z4/tIl3wo13Sqm28fRyfIsKZD+NZ8mM5RoKkpW/rBcuoSZSg==",
+      "dev": true,
+      "license": "MIT",
+      "optional": true,
+      "dependencies": {
+        "@emnapi/wasi-threads": "1.2.3",
+        "tslib": "^2.4.0"
+      }
+    },
+    "node_modules/@emnapi/core/node_modules/@emnapi/wasi-threads": {
+      "version": "1.2.3",
+      "resolved": "https://registry.npmjs.org/@emnapi/wasi-threads/-/wasi-threads-1.2.3.tgz",
+      "integrity": "sha512-ELEBe8PsLvvJ6QMr0zLt8ffvOHW/dc1m3CEzNMg7aJUv3bMaoDtw2TXyDAwkYBuroxxuHEwhRTLJSe5sya547g==",
+      "dev": true,
+      "license": "MIT",
+      "optional": true,
+      "dependencies": {
+        "tslib": "^2.4.0"
+      }
+    },
     "node_modules/@emnapi/wasi-threads": {
       "version": "1.2.2",
       "resolved": "https://registry.npmjs.org/@emnapi/wasi-threads/-/wasi-threads-1.2.2.tgz",
@@ -4589,12 +4611,6 @@
         "url": "https://paulmillr.com/funding/"
       }
     },
-    "node_modules/client-zip": {
-      "version": "2.5.0",
-      "resolved": "https://registry.npmjs.org/client-zip/-/client-zip-2.5.0.tgz",
-      "integrity": "sha512-ydG4nDZesbFurnNq0VVCp/yyomIBh+X/1fZPI/P24zbnG4dtC4tQAfI5uQsomigsUMeiRO2wiTPizLWQh+IAyQ==",
-      "license": "MIT"
-    },
     "node_modules/codemirror": {
       "version": "6.0.2",
       "resolved": "https://registry.npmmirror.com/codemirror/-/codemirror-6.0.2.tgz",