feat: add formula editor (#1484)

- Remove katex npm dependency, use existing window.MathJax instead
- Add renderWithMathJax() helper in FormulaEditorDialog for preview and snippet rendering
- Add escapeHtml to packages/core/src/utils/basicHelpers.ts
- Handle formula click in preview area to open formula editor (useCursorSync)
- Fix mobile scroll: formula library panel now scrollable on small screens
- EditorContextMenu/InsertDropdown: don't pass sourceRaw for selection-based editing, use replaceSelection() instead
- formula.ts: fix isWrapped detection to only check if unwrapFormula actually stripped delimiters
- editor.ts: replaceText() now replaces the occurrence nearest to the current cursor
- FormulaEditorDialog: cache MathJax snippet renders to avoid redundant re-renders
- katex.ts: remove unused data-math-latex attribute to reduce HTML output size


close #1483

Author: YangFong

apps/web/src/components/editor/EditorContextMenu.vue

@@ -39,6 +39,7 @@ import { useRenderStore } from '@/stores/render'
 import { useThemeStore } from '@/stores/theme'
 import { useUIStore } from '@/stores/ui'
 import { copyPlain } from '@/utils/clipboard'
+import { normalizeFormulaInput } from '@/utils/formula'
 
 const confirmStore = useConfirmStore()
 const cssEditorStore = useCssEditorStore()
@@ -85,6 +86,14 @@ function clearContent() {
   editorStore.clearContent()
 }
 
+function openFormulaEditor() {
+  const selection = normalizeFormulaInput(editorStore.getSelection())
+  uiStore.openFormulaEditor({
+    value: selection.latex,
+    displayMode: selection.displayMode,
+  })
+}
+
 // 复制到剪贴板
 async function copyToClipboard() {
   const selectedText = editorStore.getSelection()
@@ -154,6 +163,10 @@ function downloadAsCardImage() {
             <Image class="mr-2 h-4 w-4" />
             图片
           </ContextMenuItem>
+          <ContextMenuItem @click="openFormulaEditor()">
+            <span class="mr-2 inline-flex h-4 w-4 items-center justify-center text-xs font-semibold">ƒ</span>
+            公式
+          </ContextMenuItem>
           <ContextMenuItem @click="toggleShowInsertFormDialog()">
             <Table class="mr-2 h-4 w-4" />
             表格