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/hooks/__tests__/useDocStats.test.ts

@@ -0,0 +1,76 @@
+import { describe, it, expect } from 'vitest'
+import { computeDocStats } from '../useDocStats'
+
+describe('computeDocStats', () => {
+  it('should return zeros for undefined content', () => {
+    expect(computeDocStats(undefined)).toEqual({ words: 0, chars: 0, charsNoSpace: 0, lines: 0 })
+  })
+
+  it('should return zeros for null content', () => {
+    expect(computeDocStats(null)).toEqual({ words: 0, chars: 0, charsNoSpace: 0, lines: 0 })
+  })
+
+  it('should return zeros for empty string', () => {
+    expect(computeDocStats('')).toEqual({ words: 0, chars: 0, charsNoSpace: 0, lines: 0 })
+  })
+
+  it('should count single word', () => {
+    const result = computeDocStats('hello')
+    expect(result.words).toBe(1)
+    expect(result.chars).toBe(5)
+    expect(result.charsNoSpace).toBe(5)
+    expect(result.lines).toBe(1)
+  })
+
+  it('should count multiple words', () => {
+    const result = computeDocStats('hello world')
+    expect(result.words).toBe(2)
+    expect(result.chars).toBe(11) // 'hello world' = 11 chars
+    expect(result.charsNoSpace).toBe(10) // without the space
+  })
+
+  it('should count characters without spaces', () => {
+    const result = computeDocStats('a b c')
+    expect(result.chars).toBe(5)
+    expect(result.charsNoSpace).toBe(3)
+  })
+
+  it('should count lines', () => {
+    const result = computeDocStats('line1\nline2\nline3')
+    expect(result.lines).toBe(3)
+    expect(result.words).toBe(3)
+  })
+
+  it('should handle Windows line endings', () => {
+    const result = computeDocStats('line1\r\nline2\r\nline3')
+    expect(result.lines).toBe(3)
+  })
+
+  it('should handle trailing newline', () => {
+    const result = computeDocStats('hello\n')
+    expect(result.lines).toBe(2)
+    expect(result.words).toBe(1)
+  })
+
+  it('should count markdown content correctly', () => {
+    const md = '# Title\n\nThis is a **paragraph** with some *text*.\n\n- List item 1\n- List item 2\n'
+    const result = computeDocStats(md)
+    expect(result.words).toBe(17)
+    expect(result.lines).toBe(7)
+    expect(result.chars).toBe(md.length)
+  })
+
+  it('should handle whitespace-only content', () => {
+    const result = computeDocStats('   \n  \n  ')
+    expect(result.words).toBe(0)
+    expect(result.chars).toBe(9)
+    expect(result.charsNoSpace).toBe(0)
+    expect(result.lines).toBe(3)
+  })
+
+  it('should handle content with non-ASCII characters', () => {
+    const result = computeDocStats('中文测试 日本語 한국어')
+    expect(result.words).toBe(3)
+    expect(result.chars).toBe(12)
+  })
+})

src/renderer/hooks/useDocStats.ts

@@ -0,0 +1,39 @@
+import { useMemo } from 'react'
+
+export interface DocStats {
+  /** 单词数（按空白字符分割） */
+  words: number
+  /** 总字符数（含空白字符） */
+  chars: number
+  /** 字符数（不含空白字符） */
+  charsNoSpace: number
+  /** 行数 */
+  lines: number
+}
+
+/**
+ * 计算文档统计信息：单词数、字符数（含/不含空格）、行数。
+ * 对空文档或 undefined 返回全零值。
+ */
+export function computeDocStats(content: string | undefined | null): DocStats {
+  if (!content) {
+    return { words: 0, chars: 0, charsNoSpace: 0, lines: 0 }
+  }
+
+  const chars = content.length
+  const charsNoSpace = content.replace(/\s/g, '').length
+  const words = content.trim()
+    ? content.trim().split(/\s+/).length
+    : 0
+  const lines = content === '' ? 0 : content.split(/\r?\n/).length
+
+  return { words, chars, charsNoSpace, lines }
+}
+
+/**
+ *  Hook：根据文档内容实时计算统计信息。
+ *  使用 useMemo 避免不必要的重新计算。
+ */
+export function useDocStats(content: string | undefined | null): DocStats {
+  return useMemo(() => computeDocStats(content), [content])
+}

src/renderer/hooks/useFileOperations.ts

@@ -70,7 +70,7 @@ export function useFileOperations(showToast: (msg: string, type?: ToastType) =>
     setLoading('file-open', true)
     try {
       const result = await window.electronAPI.readFile(filePath)
-      if (result.success) {
+      if (result.success && result.content !== undefined) {
         createTab(filePath, result.content)
         recentFilesRepository.add(filePath)
         setTimeout(() => useTabStore.getState().saveToDB(), 100)