重构：文件系统模块化架构，增强 Markdown 渲染

- 拆分 FileSystem.vue 为模块化组件架构
- 新增 Markdown Mermaid 图表渲染支持
- 新增 180+ 编程语言代码高亮
- 修复编辑/预览模式切换渲染问题
- 优化亮色/暗色模式主题适配
- 新增 TypeScript 类型定义

internal/filesystem/content_detector.go

@@ -0,0 +1,133 @@
+package filesystem
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+)
+
+const maxDetectSize = 500 * 1024 // 500KB
+
+// FileTypeInfo 文件类型信息
+type FileTypeInfo struct {
+	Extension string  `json:"extension"`
+	Category  string  `json:"category"`  // image, text, binary
+	MIMEType  string  `json:"mime_type"`
+	Confidence float64 `json:"confidence"`
+}
+
+// 常见文件魔数
+var magicNumbers = []struct {
+	magic    []byte
+	ext      string
+	category string
+	mime     string
+}{
+	// 图片
+	{[]byte{0xFF, 0xD8, 0xFF}, "jpg", "image", "image/jpeg"},
+	{[]byte{0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A}, "png", "image", "image/png"},
+	{[]byte{0x47, 0x49, 0x46, 0x38}, "gif", "image", "image/gif"},
+	{[]byte{0x42, 0x4D}, "bmp", "image", "image/bmp"},
+	{[]byte{0x57, 0x45, 0x42, 0x50}, "webp", "image", "image/webp"},
+
+	// 文档
+	{[]byte{0x25, 0x50, 0x44, 0x46}, "pdf", "pdf", "application/pdf"},
+
+	// 压缩
+	{[]byte{0x50, 0x4B, 0x03, 0x04}, "zip", "archive", "application/zip"},
+}
+
+// DetectFileTypeByContent 通过文件内容检测文件类型
+func (s *FileSystemService) DetectFileTypeByContent(path string) (*FileTypeInfo, error) {
+	if err := s.validatePath(path); err != nil {
+		return nil, fmt.Errorf("路径验证失败: %w", err)
+	}
+
+	info, err := os.Stat(path)
+	if err != nil {
+		return nil, fmt.Errorf("无法访问文件: %w", err)
+	}
+
+	if info.Size() > maxDetectSize {
+		return &FileTypeInfo{Category: "unknown", Confidence: 0}, nil
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("读取文件失败: %w", err)
+	}
+
+	// 检测魔数
+	for _, m := range magicNumbers {
+		if len(data) >= len(m.magic) && bytes.Equal(data[:len(m.magic)], m.magic) {
+			return &FileTypeInfo{
+				Extension:  m.ext,
+				Category:   m.category,
+				MIMEType:   m.mime,
+				Confidence: 0.95,
+			}, nil
+		}
+	}
+
+	// 检测是否为文本
+	if isTextContent(data) {
+		return &FileTypeInfo{
+			Extension:  "txt",
+			Category:   "text",
+			MIMEType:   "text/plain",
+			Confidence: 0.8,
+		}, nil
+	}
+
+	return &FileTypeInfo{
+		Extension:  "",
+		Category:   "binary",
+		MIMEType:   "application/octet-stream",
+		Confidence: 0.5,
+	}, nil
+}
+
+// isTextContent 检测是否为文本内容
+func isTextContent(data []byte) bool {
+	if len(data) == 0 {
+		return false
+	}
+
+	textBytes := 0
+	for _, b := range data[:min(len(data), 512)] {
+		if b == 9 || b == 10 || b == 13 || (b >= 32 && b <= 126) {
+			textBytes++
+		} else if b == 0 {
+			return false
+		}
+	}
+
+	return float64(textBytes)/float64(min(len(data), 512)) > 0.9
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+// DetectFileTypeByContentSimple 简化接口
+func DetectFileTypeByContentSimple(path string) (map[string]interface{}, error) {
+	service, err := GetGlobalService()
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := service.DetectFileTypeByContent(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return map[string]interface{}{
+		"extension":  info.Extension,
+		"category":   info.Category,
+		"mime_type":  info.MIMEType,
+		"confidence": info.Confidence,
+	}, nil
+}