feat(editor): add inline autocomplete suggestions

Add GhostTextOverlay component for displaying AI-powered completion
suggestions while typing. Includes accept and dismiss actions triggered
by API calls to /v1/completions endpoint with prefix/suffix context.

src/components/MarkdownEditor.vue

@@ -1,5 +1,14 @@
 <template>
   <div class="editor-wrapper" ref="wrapperRef">
+    <!-- Ghost Text 建议覆盖层 -->
+    <GhostTextOverlay
+      v-if="suggestion"
+      :suggestion="suggestion"
+      :position="suggestionPosition"
+      @accept="acceptSuggestion"
+      @dismiss="dismissSuggestion"
+    />
+
     <!-- 单栏编辑器 -->
     <div
       ref="editorRef"
@@ -44,9 +53,12 @@
 import { ref, watch, onMounted, nextTick } from 'vue'
 import { plugins } from '../plugins/index'
 import PluginHost from './PluginHost.vue'
+import GhostTextOverlay from './GhostTextOverlay.vue'
 import markdownIt from 'markdown-it'
 import Prism from 'prismjs'
 
+const API_URL = import.meta.env.VITE_API_URL || 'http://localhost:8000'
+
 const emit = defineEmits(['update:html'])
 
 /* ---------- 插件挂载点 ---------- */
@@ -83,22 +95,88 @@ const editingCodeBlock = ref(false)
 const codeBlockContent = ref('')
 const currentCodeElement = ref(null)
 
+/* ---------- Ghost Text 建议 ---------- */
+const suggestion = ref('')
+const suggestionPosition = ref({ left: 0, top: 0 })
+let completionController = null
+
 /* ---------- 图片预览 ---------- */
 const expandedImage = ref(null)
 
 /* ---------- 光标位置管理 ---------- */
+function getCursorPosition() {
+  const sel = window.getSelection()
+  if (!sel.rangeCount || !editorRef.value) return null
+  
+  try {
+    const range = sel.getRangeAt(0)
+    if (!range) return null
+    
+    // 检查是否在代码块内（使用 commonAncestorContainer.closest）
+    const container = range.commonAncestorContainer
+    const codeBlock = container.nodeType === Node.ELEMENT_NODE
+      ? container.closest('pre')
+      : container.parentElement?.closest('pre')
+    if (codeBlock) {
+      return { type: 'code', element: codeBlock }
+    }
+    
+    // 获取光标位置的坐标
+    const rect = range.getBoundingClientRect()
+    const editorRect = editorRef.value.getBoundingClientRect()
+    
+    return {
+      type: 'text',
+      range: range.cloneRange(),
+      left: rect.left - editorRect.left,
+      top: rect.top - editorRect.top + window.scrollY
+    }
+  } catch (e) {
+    console.error('getCursorPosition error:', e)
+    return null
+  }
+}
+
+function getPrefixSuffix(cursorRange) {
+  const fullText = markdown.value
+  if (!cursorRange || !cursorRange.range) return { prefix: fullText, suffix: '' }
+  
+  // 获取光标在纯文本中的位置
+  const preCaretRange = cursorRange.range.cloneRange()
+  preCaretRange.selectNodeContents(editorRef.value)
+  preCaretRange.setEnd(cursorRange.range.startContainer, cursorRange.range.startOffset)
+  const prefix = preCaretRange.toString()
+  
+  // 获取 suffix（光标后的内容）
+  const postCaretRange = cursorRange.range.cloneRange()
+  postCaretRange.setStartAfter(cursorRange.range.endContainer, cursorRange.range.endOffset)
+  const suffix = postCaretRange.toString()
+  
+  return { prefix, suffix }
+}
+
 function saveSelection() {
   const sel = window.getSelection()
   if (!sel.rangeCount) return null
-  const range = sel.getRangeAt(0)
   
-  // 检查是否在代码块内
-  const codeBlock = range.closest('pre')
-  if (codeBlock) {
-    return { type: 'code', element: codeBlock }
+  try {
+    const range = sel.getRangeAt(0)
+    if (!range) return null
+    
+    // 检查是否在代码块内
+    const container = range.commonAncestorContainer
+    const codeBlock = container.nodeType === Node.ELEMENT_NODE
+      ? container.closest('pre')
+      : container.parentElement?.closest('pre')
+    if (codeBlock) {
+      return { type: 'code', element: codeBlock }
+    }
+    
+    return { type: 'text', range: range.cloneRange() }
+  } catch (e) {
+    console.error('saveSelection error:', e)
+    return null
   }
-  
-  return { type: 'text', range: range.cloneRange() }
 }
 
 function restoreSelection(saved) {
@@ -117,6 +195,83 @@ function restoreSelection(saved) {
   } catch (e) {}
 }
 
+/* ---------- Ghost Text 请求 ---------- */
+async function requestCompletion(prefix, suffix) {
+  if (completionController) {
+    completionController.abort()
+  }
+  
+  try {
+    completionController = new AbortController()
+    const response = await fetch(`${API_URL}/v1/completions`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ prefix, suffix, languageId: 'markdown' }),
+      signal: completionController.signal
+    })
+    
+    if (!response.ok) throw new Error('Completion request failed')
+    
+    const reader = response.body.getReader()
+    const decoder = new TextDecoder()
+    let content = ''
+    
+    while (true) {
+      const { done, value } = await reader.read()
+      if (done) break
+      const chunk = decoder.decode(value)
+      const lines = chunk.split('\n').filter(l => l.startsWith('data: '))
+      
+      for (const line of lines) {
+        try {
+          const data = JSON.parse(line.slice(6))
+          if (data.content) content += data.content
+          if (data.done) break
+        } catch {}
+      }
+    }
+    
+    return content
+  } catch (e) {
+    if (e.name !== 'AbortError') console.error('Completion error:', e)
+    return ''
+  }
+}
+
+async function onInput(e) {
+  isEditing.value = true
+  const content = getPlainText()
+  markdown.value = content
+  
+  clearTimeout(debounceTimer)
+  debounceTimer = setTimeout(async () => {
+    renderMarkdown()
+    
+    // 请求补全建议
+    const cursorPos = getCursorPosition()
+    if (cursorPos && cursorPos.type === 'text') {
+      const { prefix, suffix } = getPrefixSuffix(cursorPos)
+      suggestion.value = await requestCompletion(prefix, suffix)
+      if (suggestion.value) {
+        suggestionPosition.value = { left: cursorPos.left, top: cursorPos.top }
+      }
+    }
+    
+    isEditing.value = false
+  }, 300)
+}
+
+function acceptSuggestion() {
+  if (!suggestion.value) return
+  insertAtCursor(suggestion.value)
+  suggestion.value = ''
+  onInput()
+}
+
+function dismissSuggestion() {
+  suggestion.value = ''
+}
+
 /* ---------- 防抖渲染 ---------- */
 function renderMarkdown() {
   let html = md.render(markdown.value)
@@ -145,18 +300,6 @@ function renderMarkdown() {
   })
 }
 
-function onInput(e) {
-  isEditing.value = true
-  // 获取纯文本内容（排除 HTML 标签）
-  const content = getPlainText()
-  markdown.value = content
-  
-  clearTimeout(debounceTimer)
-  debounceTimer = setTimeout(() => {
-    renderMarkdown()
-    isEditing.value = false
-  }, 300)
-}
 
 /* ---------- 从 contenteditable 获取纯文本 ---------- */
 function getPlainText() {