fix(builder): improve artifact packaging with optional helper support

Update move_first_existing function to handle optional artifacts gracefully
instead of raising FileNotFoundError. When optional artifacts are missing,
append informative messages to stdout_err instead of failing the build.

Also update agent icons to reference external PNG files instead of embedded
base64 data for better maintainability.

Payload_Type/ares/ares/mythic/agent_functions/builder.py

@@ -648,12 +648,17 @@ NOTE: v2.3.2+ uses a different BOF loader than v2.3.1 and they are not compatibl
                     StepSuccess=True
                 ))
                 resp.status = BuildStatus.Success
-                def move_first_existing(candidates, target_path):
+                missing_optional_artifacts = []
+
+                def move_first_existing(candidates, target_path, required=False):
                     for candidate in candidates:
                         if os.path.exists(candidate):
                             shutil.move(candidate, target_path)
-                            return
-                    raise FileNotFoundError(f"Unable to locate artifact for {target_path}: {candidates}")
+                            return True
+                    if required:
+                        raise FileNotFoundError(f"Unable to locate artifact for {target_path}: {candidates}")
+                    missing_optional_artifacts.append((target_path, candidates))
+                    return False
 
                 targetExeAsmPath = "/srv/ExecuteAssembly.exe"
                 targetPowerPickPath = "/srv/PowerShellHost.exe"
@@ -685,6 +690,10 @@ NOTE: v2.3.2+ uses a different BOF loader than v2.3.1 and they are not compatibl
                     f"{agent_build_path.name}/{buildPath}/AresInterop.dll",
                     f"{agent_build_path.name}/AresInterop/bin/Release/net451/AresInterop.dll",
                 ], targetInteropPath)
+                if missing_optional_artifacts:
+                    stdout_err += "\nOptional helper artifacts were not packaged:\n" + "\n".join(
+                        f"{target}: {candidates}" for target, candidates in missing_optional_artifacts
+                    )
                 if self.get_parameter('output_type') == "Source":
                     shutil.make_archive(f"/tmp/{agent_build_path.name}/source", "zip", f"{agent_build_path.name}")
                     await SendMythicRPCPayloadUpdatebuildStep(MythicRPCPayloadUpdateBuildStepMessage(