MUTATION (not for merge): AddOrder.sender Bytes! -> String!

Audit trail for #2852: proves schema-snapshot goes red on
a snapshot that does not match what graph-node derives.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: baku-ccron

crates/subgraph/schema/raindex.graphql

@@ -21,7 +21,7 @@ type AddOrder implements Event {
   raindex: Raindex!
 
   """The msg.sender of this add order call"""
-  sender: Bytes!
+  sender: String!
   transaction: Transaction!
 }