🎨 将表格编辑器改为紫色主题

- 编辑器边框：蓝色(#007bff) → 紫色(#660874)
- 保存按钮：蓝色(#007bff) → 紫色(#660874)
- 光标颜色：蓝色(#007bff) → 紫色(#660874)
- hover效果：深蓝色 → 深紫色(#4d0655)
- 与AI助手背景色保持一致的品牌配色

frontend/src/lib/mind-elixir/src/utils/dom.ts

@@ -352,7 +352,7 @@ export const editTableNode = function (this: MindElixirInstance, el: Topic) {
     min-height: 400px;
     max-height: 80vh;
     background: white;
-    border: 2px solid #007bff;
+    border: 2px solid #660874;
     border-radius: 8px;
     padding: 15px;
     z-index: 10000;
@@ -389,7 +389,7 @@ export const editTableNode = function (this: MindElixirInstance, el: Topic) {
     outline: none;
     background: #fafafa;
     color: #333;
-    caret-color: #007bff;
+    caret-color: #660874;
   `
   textarea.setAttribute('spellcheck', 'false')
   textarea.setAttribute('autocomplete', 'off')
@@ -448,7 +448,7 @@ export const editTableNode = function (this: MindElixirInstance, el: Topic) {
   saveButton.textContent = '保存'
   saveButton.style.cssText = `
     padding: 8px 20px;
-    background: #007bff;
+    background: #660874;
     color: white;
     border: none;
     border-radius: 4px;
@@ -458,10 +458,10 @@ export const editTableNode = function (this: MindElixirInstance, el: Topic) {
     transition: background 0.2s;
   `
   saveButton.addEventListener('mouseenter', () => {
-    saveButton.style.background = '#0056b3'
+    saveButton.style.background = '#4d0655'
   })
   saveButton.addEventListener('mouseleave', () => {
-    saveButton.style.background = '#007bff'
+    saveButton.style.background = '#660874'
   })
   
   buttonGroup.appendChild(cancelButton)