Make Hysteria UDP port selectable when 443 is busy.

Show an inline port field on the stopped card, a dedicated install port, and clearer bind-error hints so admins can switch to 8998/8443 without guessing.

Co-authored-by: Cursor <cursoragent@cursor.com>

app.py

@@ -2708,6 +2708,13 @@ async def api_check_server(request: Request, server_id: int):
                 for key in ('domain', 'email', 'site_url'):
                     if db_proto.get(key) not in (None, ''):
                         merged[key] = db_proto[key]
+            if protocol_base(proto) == 'hysteria':
+                for key in ('domain', 'email'):
+                    if db_proto.get(key) not in (None, '') and not merged.get(key):
+                        merged[key] = db_proto[key]
+                # Keep a useful error even when merging preserved records
+                if db_proto.get('port') and not merged.get('port'):
+                    merged['port'] = db_proto['port']
             return merged
 
         def should_preserve_saved_protocol(proto, result=None, err=None):