feat: add xmlsvg export option (#761)

* feat: add xmlsvg export option

* fix: avoid atob for xmlsvg export to prevent UTF-8 corruption

Pass the data URL directly (like PNG export) instead of decoding
with atob(). atob() + Blob([string]) double-encodes non-ASCII
characters (Chinese, Japanese, emoji), corrupting the output file.

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

components/save-dialog.tsx

@@ -20,7 +20,7 @@ import {
 } from "@/components/ui/select"
 import { useDictionary } from "@/hooks/use-dictionary"
 
-export type ExportFormat = "drawio" | "png" | "svg"
+export type ExportFormat = "drawio" | "png" | "svg" | "xmlsvg"
 
 interface SaveDialogProps {
     open: boolean
@@ -74,6 +74,11 @@ export function SaveDialog({
             label: dict.save.formats.svg,
             extension: ".svg",
         },
+        {
+            value: "xmlsvg" as const,
+            label: dict.save.formats.xmlsvg,
+            extension: ".drawio.svg",
+        },
     ]
 
     const currentFormat = FORMAT_OPTIONS.find((f) => f.value === format)