fix(external_editor): cache auto-detect result, avoid hitting registry on every UI frame

remove_bom.py

@@ -0,0 +1,11 @@
+import sys
+with open('config.toml', 'rb') as f:
+    data = f.read()
+BOM = bytes([0xef, 0xbb, 0xbf])
+if data.startswith(BOM):
+    with open('config.toml', 'wb') as f:
+        f.write(data[3:])
+    print('BOM removed')
+else:
+    print('No BOM found')
+sys.exit(0)