Add region management

This adds region management: the user can manage a list of available regions
and for each channel pick a region from that list to apply to messages.

Region discovery from nearby repeaters will be done in a separate PR.

This is a part of the work needed for #120.

lib/connector/meshcore_protocol.dart

@@ -1,6 +1,7 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
+import 'package:crypto/crypto.dart' as crypto;
 import 'package:flutter/widgets.dart';
 
 // Buffer Reader - sequential binary data reader with pointer tracking
@@ -211,6 +212,7 @@ const int cmdSendAnonReq = 57;
 const int cmdSetAutoAddConfig = 58;
 const int cmdGetAutoAddConfig = 59;
 const int cmdSetPathHashMode = 61;
+const int cmdSetFloodScope = 54;
 
 // Text message types
 const int txtTypePlain = 0;
@@ -955,3 +957,18 @@ Uint8List buildSendTelemetryReq(Uint8List? pubKey) {
   }
   return writer.toBytes();
 }
+
+//Build CMD_SET_FLOOD_SCOPE
+// Format: [cmd][scope]
+Uint8List buildSetFloodScopeFrame(String region) {
+  if (region == '') {
+    // reset scope
+    return Uint8List.fromList([cmdSetFloodScope, 0]);
+  }
+
+  final name = region.startsWith('#') ? region : '#$region';
+  final hash = crypto.sha256.convert(utf8.encode(name)).bytes;
+  final scope = Uint8List.fromList(hash.sublist(0, 16));
+
+  return Uint8List.fromList([cmdSetFloodScope, 0, ...scope]);
+}