feat: Add agentCard method to ProtoUtils.FromProto

Added ProtoUtils.FromProto.agentCard() method to convert io.a2a.grpc.AgentCard to io.a2a.spec.AgentCard.

- Follows the same pattern as other FromProto methods (handles both concrete and builder types)
- Uses AgentCardMapper.INSTANCE.fromProto() for the conversion
- Positioned at the start of FromProto class for consistency with ToProto ordering

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ehsavoie

spec-grpc/src/main/java/io/a2a/grpc/utils/ProtoUtils.java

@@ -184,6 +184,13 @@ public static io.a2a.grpc.StreamResponse taskOrMessageStream(StreamingEventKind
 
     public static class FromProto {
 
+        public static AgentCard agentCard(io.a2a.grpc.AgentCardOrBuilder agentCard) {
+            io.a2a.grpc.AgentCard agentCardProto = agentCard instanceof io.a2a.grpc.AgentCard
+                    ? (io.a2a.grpc.AgentCard) agentCard
+                    : ((io.a2a.grpc.AgentCard.Builder) agentCard).build();
+            return AgentCardMapper.INSTANCE.fromProto(agentCardProto);
+        }
+
         public static TaskQueryParams taskQueryParams(io.a2a.grpc.GetTaskRequestOrBuilder request) {
             io.a2a.grpc.GetTaskRequest reqProto = request instanceof io.a2a.grpc.GetTaskRequest
                     ? (io.a2a.grpc.GetTaskRequest) request