fix: support Gitea 28.0.0 mail templates

tools/preview/funcs.go

@@ -15,10 +15,10 @@ var TemplateFuncs = template.FuncMap{
 	"QueryEscape":        url.QueryEscape,
 	"ShortSha":           ShortSha,
 	"PathEscapeSegments": PathEscapeSegments,
-	"FileSize":           FileSize,
+	"FormatByteSize":     previewFormatByteSize,
 	"HTMLFormat":         HTMLFormat,
 	"Dict":               Dict,
-	"gt":                 Gt,  // override built-in for JSON float64/int coercion
+	"gt":                 Gt, // override built-in for JSON float64/int coercion
 	"lt":                 Lt,
 	"ge":                 Ge,
 	"le":                 Le,
@@ -41,8 +41,20 @@ func PathEscapeSegments(s string) string {
 	return strings.Join(parts, "/")
 }
 
-// FileSize formats a byte count as a human-readable string (e.g. "2.5 MB").
-func FileSize(n int64) string {
+// previewFormatByteSize converts JSON fixture numbers to Gitea's int64 input type.
+func previewFormatByteSize(size any) (string, error) {
+	switch n := size.(type) {
+	case int64:
+		return FormatByteSize(n), nil
+	case float64:
+		return FormatByteSize(int64(n)), nil
+	default:
+		return "", fmt.Errorf("FormatByteSize: unsupported size type %T", size)
+	}
+}
+
+// FormatByteSize mirrors Gitea 28's IEC attachment size formatting.
+func FormatByteSize(n int64) string {
 	const unit = 1024
 	if n < unit {
 		return fmt.Sprintf("%d B", n)
@@ -52,7 +64,7 @@ func FileSize(n int64) string {
 		div *= unit
 		exp++
 	}
-	return fmt.Sprintf("%.1f %s", float64(n)/float64(div), []string{"KB", "MB", "GB", "TB"}[exp])
+	return fmt.Sprintf("%.1f %s", float64(n)/float64(div), []string{"KiB", "MiB", "GiB", "TiB"}[exp])
 }
 
 // HTMLFormat substitutes %s/%d placeholders with HTML-escaped values.