refactor(后台富文本): 编辑器从 wangEditor 换成 Tiptap，老题面的图片尺寸、缩进、颜色打开再保存都不丢

拿库里全部 3384 条题面 / 提示 / 公告 / 比赛说明做过往返比对，补上图片 style、base64 图片、
段落缩进三处后文字和格式都对得上。工具栏照画布做成一行浅灰小图标，四套档位不变，
加了行内代码、光标在表格里出加删行列。表格格子里的段落在学生端不再把行撑高。
编辑器 JS 638 kB → 455 kB，wangEditor 的 39 kB 样式不用了；polyfill 清单重新审过，
去掉只有 wangEditor 用到的 web.immediate。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/package.json

@@ -22,10 +22,16 @@
     "@codemirror/view": "^6.43.14",
     "@lezer/highlight": "^1.2.5",
     "@oj2/contract": "workspace:*",
+    "@tiptap/core": "3.32.0",
+    "@tiptap/extension-image": "3.32.0",
+    "@tiptap/extension-table": "3.32.0",
+    "@tiptap/extension-text-align": "3.32.0",
+    "@tiptap/extension-text-style": "3.32.0",
+    "@tiptap/pm": "3.32.0",
+    "@tiptap/starter-kit": "3.32.0",
+    "@tiptap/vue-3": "3.32.0",
     "@vueuse/core": "^15.0.0",
     "@vueuse/router": "^15.0.0",
-    "@wangeditor-next/editor": "^6.5.0",
-    "@wangeditor-next/editor-for-vue": "^6.5.0",
     "canvas-confetti": "^1.9.4",
     "chart.js": "^4.5.1",
     "chartjs-chart-wordcloud": "^4.4.5",