fix: improve version field detection regex to handle any field order

Changed the regex pattern from checking only immediately after the opening
brace to checking anywhere in the JSON. This handles valid JSON where the
'version' field appears after other fields like 'bomFormat' or 'specVersion'.

Pattern changed from: ^\s*\{\s*"version"\s*:
To: "version"\s*:\s*\d+

This prevents incorrectly adding duplicate version fields when the field
already exists but not at the beginning of the JSON object.

Author: claude

src/CycloneDX.MSBuild/build/CycloneDX.MSBuild.targets

@@ -160,16 +160,16 @@
         {
             var jsonContent = File.ReadAllText(SbomPath);
 
-            // Simple check if version field already exists using regex
-            // Look for "version" field at the root level (after opening brace, before other fields)
-            var versionPattern = @"^\s*\{\s*""version""\s*:";
-            if (Regex.IsMatch(jsonContent, versionPattern, RegexOptions.Multiline))
+            // Check if version field exists anywhere in the JSON (not just at the beginning)
+            // This handles cases where version appears after other fields like bomFormat or specVersion
+            var versionPattern = @"""version""\s*:\s*\d+";
+            if (Regex.IsMatch(jsonContent, versionPattern))
             {
                 Log.LogMessage(MessageImportance.Low, "[CycloneDX] SBOM already has version field");
             }
             else
             {
-                // Version field doesn't exist, add it
+                // Version field doesn't exist, add it after the opening brace
                 // Find the opening brace and insert version field right after it
                 var insertPattern = @"^(\s*\{)\s*$";
                 var replacement = "$1\n  \"version\": 1,";