feat: add contact UI helpers and path editor for routing management

- Implemented contactTypeIcon and contactTypeColor functions for better UI representation of contact types.
- Created colorForName and firstCharacterOrEmoji functions to enhance contact display.
- Developed PathEditorSheet widget for managing contact paths with a user-friendly interface.
- Introduced RoutingSheet for managing contact routing modes and displaying path history.
- Added a script for generating proof of concept (PoC) payloads for clipboard contact import validation.

lib/connector/meshcore_protocol.dart

@@ -457,8 +457,13 @@ String pubKeyToHex(Uint8List pubKey) {
 
 // Helper to convert hex string to public key
 Uint8List hexToPubKey(String hex) {
+  if (hex.length != pubKeySize * 2) {
+    throw FormatException(
+      'Public key hex must be ${pubKeySize * 2} chars, got ${hex.length}',
+    );
+  }
   final result = Uint8List(pubKeySize);
-  for (int i = 0; i < pubKeySize && i * 2 + 1 < hex.length; i++) {
+  for (int i = 0; i < pubKeySize; i++) {
     result[i] = int.parse(hex.substring(i * 2, i * 2 + 2), radix: 16);
   }
   return result;