✨ feat(font): 新增系统字体枚举与全局字体配置能力

- 新增 Go 侧已安装字体扫描接口，支持前端读取系统真实字体列表
- 接入 Wails 字体查询导出，补齐 App.d.ts 与 App.js 调用声明
- 新增字体选项构建与匹配工具，区分 UI 字体与等宽字体候选
- 外观设置支持按平台加载字体列表，并支持搜索匹配与默认字体回退
- Store 增加自定义 UI 字体与代码字体配置，持久化全局字体选择

internal/app/methods_fonts.go

@@ -0,0 +1,172 @@
+package app
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"runtime"
+	"sort"
+	"strings"
+
+	"GoNavi-Wails/internal/connection"
+
+	"golang.org/x/image/font/sfnt"
+)
+
+const maxScannedFontFiles = 4096
+
+type installedFontFamily struct {
+	Family string `json:"family"`
+	Path   string `json:"path,omitempty"`
+}
+
+func (a *App) ListInstalledFontFamilies() connection.QueryResult {
+	families, err := listInstalledFontFamilies()
+	if err != nil {
+		return connection.QueryResult{
+			Success: false,
+			Message: err.Error(),
+		}
+	}
+	return connection.QueryResult{
+		Success: true,
+		Data:    families,
+	}
+}
+
+func listInstalledFontFamilies() ([]installedFontFamily, error) {
+	fontPaths := resolveSystemFontDirs()
+	if len(fontPaths) == 0 {
+		return []installedFontFamily{}, nil
+	}
+
+	seenDirs := make(map[string]struct{}, len(fontPaths))
+	familyByName := make(map[string]installedFontFamily)
+	scannedFiles := 0
+
+	for _, rawDir := range fontPaths {
+		dir := strings.TrimSpace(rawDir)
+		if dir == "" {
+			continue
+		}
+		absDir, err := filepath.Abs(dir)
+		if err != nil {
+			absDir = dir
+		}
+		cleanDir := filepath.Clean(absDir)
+		if _, ok := seenDirs[cleanDir]; ok {
+			continue
+		}
+		seenDirs[cleanDir] = struct{}{}
+
+		info, err := os.Stat(cleanDir)
+		if err != nil || !info.IsDir() {
+			continue
+		}
+
+		walkErr := filepath.WalkDir(cleanDir, func(path string, d os.DirEntry, walkErr error) error {
+			if walkErr != nil {
+				return nil
+			}
+			if d.IsDir() {
+				return nil
+			}
+			if scannedFiles >= maxScannedFontFiles {
+				return fs.SkipAll
+			}
+			if !isFontFile(path) {
+				return nil
+			}
+			scannedFiles++
+			family := readFontFamilyName(path)
+			if family == "" {
+				return nil
+			}
+			if _, exists := familyByName[family]; exists {
+				return nil
+			}
+			familyByName[family] = installedFontFamily{
+				Family: family,
+				Path:   path,
+			}
+			return nil
+		})
+		if walkErr == fs.SkipAll {
+			break
+		}
+	}
+
+	result := make([]installedFontFamily, 0, len(familyByName))
+	for _, item := range familyByName {
+		result = append(result, item)
+	}
+	sort.Slice(result, func(i, j int) bool {
+		return strings.ToLower(result[i].Family) < strings.ToLower(result[j].Family)
+	})
+	return result, nil
+}
+
+func resolveSystemFontDirs() []string {
+	switch runtime.GOOS {
+	case "darwin":
+		home, _ := os.UserHomeDir()
+		return []string{
+			"/System/Library/Fonts",
+			"/Library/Fonts",
+			filepath.Join(home, "Library", "Fonts"),
+		}
+	case "windows":
+		winDir := os.Getenv("WINDIR")
+		localAppData := os.Getenv("LOCALAPPDATA")
+		return []string{
+			filepath.Join(winDir, "Fonts"),
+			filepath.Join(localAppData, "Microsoft", "Windows", "Fonts"),
+		}
+	default:
+		home, _ := os.UserHomeDir()
+		return []string{
+			"/usr/share/fonts",
+			"/usr/local/share/fonts",
+			filepath.Join(home, ".fonts"),
+			filepath.Join(home, ".local", "share", "fonts"),
+		}
+	}
+}
+
+func isFontFile(path string) bool {
+	ext := strings.ToLower(filepath.Ext(path))
+	switch ext {
+	case ".ttf", ".otf", ".ttc", ".otc":
+		return true
+	default:
+		return false
+	}
+}
+
+func readFontFamilyName(path string) string {
+	file, err := os.Open(path)
+	if err != nil {
+		return ""
+	}
+	defer func() { _ = file.Close() }()
+
+	collection, err := sfnt.ParseCollectionReaderAt(file)
+	if err != nil {
+		return ""
+	}
+	var buf sfnt.Buffer
+	fontCount := collection.NumFonts()
+	for i := range fontCount {
+		font, fontErr := collection.Font(i)
+		if fontErr != nil {
+			continue
+		}
+		for _, nameID := range []sfnt.NameID{sfnt.NameIDTypographicFamily, sfnt.NameIDFamily} {
+			family, nameErr := font.Name(&buf, nameID)
+			if nameErr == nil && strings.TrimSpace(family) != "" {
+				return strings.TrimSpace(family)
+			}
+		}
+	}
+	return ""
+}