v0.3.5: Bug修复+性能优化+状态栏文档统计

Bug修复:
- BUG-01: Sidebar norm函数正则修复(单反斜杠匹配), Windows路径规范化恢复
- BUG-02: 3处result.content truthy检查改为content !== undefined, 空文件可打开
- BUG-03: TAB_SWITCHED路径校验顺序修复, activeFilePath不在校验前写入

优化:
- OPT-01: Sidebar handleFileClick添加loading状态, 打开文件有视觉反馈

新功能:
- FEAT-01: 状态栏添加行数/单词数/字符数统计
  - useDocStats hook + computeDocStats 纯函数
  - StatusBar右侧显示 行/词/字符 统计信息
  - 12个单元测试覆盖空值/空白/ASCII/UTF-8/Markdown等场景

验证: TS 0错误, ESLint 0错误(1个预存警告), 90/90测试通过

src/renderer/components/StatusBar/StatusBar.tsx

@@ -1,12 +1,14 @@
 import React from 'react'
 import { useTabStore } from '../../stores/tabStore'
 import { useEditorStore } from '../../stores/editorStore'
+import { useDocStats } from '../../hooks/useDocStats'
 import { getFileName } from '../../lib/fileUtils'
 import { LoadingSpinner } from '../LoadingSpinner/LoadingSpinner'
 
 export const StatusBar = React.memo(function StatusBar() {
   const activeTab = useTabStore(s => s.getActiveTab())
   const loadingStates = useEditorStore(s => s.loadingStates)
+  const stats = useDocStats(activeTab?.content)
 
   // 判断是否有任何加载状态激活
   const hasLoading = Object.values(loadingStates).some(Boolean)
@@ -32,6 +34,22 @@ export const StatusBar = React.memo(function StatusBar() {
         </span>
       </div>
       <div className="status-right">
+        {activeTab && (
+          <>
+            <span className="status-stat" title="行数" aria-label={`${stats.lines} 行`}>
+              {stats.lines} 行
+            </span>
+            <span className="status-divider">|</span>
+            <span className="status-stat" title="单词数" aria-label={`${stats.words} 个单词`}>
+              {stats.words} 词
+            </span>
+            <span className="status-divider">|</span>
+            <span className="status-stat" title="字符数（含空格）" aria-label={`${stats.chars} 个字符`}>
+              {stats.chars} 字符
+            </span>
+            <span className="status-divider">|</span>
+          </>
+        )}
         <span id="status-encoding">UTF-8</span>
         <span className="status-divider">|</span>
         <span id="status-lang">Markdown</span>