Fix migrate export crash on non-ASCII server names in download headers.

app.py

@@ -227,6 +227,17 @@ def get_server_connect_host(server: dict, protocol: Optional[str] = None) -> str
     return (server.get('host') or '').strip()
 
 
+def _ascii_filename_component(value: str, *, fallback: str = 'file') -> str:
+    """HTTP headers are latin-1; keep only ASCII for Content-Disposition filenames."""
+    text = str(value or '').strip()
+    # NFKD strip accents, then drop non-ASCII leftovers (e.g. Cyrillic names).
+    import unicodedata
+    text = unicodedata.normalize('NFKD', text)
+    text = text.encode('ascii', 'ignore').decode('ascii')
+    text = re.sub(r'[^A-Za-z0-9._-]+', '_', text).strip('._-')
+    return text or fallback
+
+
 def get_current_user(request: Request, data: Optional[dict] = None):
     user_id = request.session.get('user_id')
     if not user_id: