Add call graph fixtures for various languages and scenarios

- Introduced `all-edge-reasons.json` to test edge resolution reasons in .NET.
- Added `all-visibility-levels.json` to validate method visibility levels in .NET.
- Created `dotnet-aspnetcore-minimal.json` for a minimal ASP.NET Core application.
- Included `go-gin-api.json` for a Go Gin API application structure.
- Added `java-spring-boot.json` for the Spring PetClinic application in Java.
- Introduced `legacy-no-schema.json` for legacy application structure without schema.
- Created `node-express-api.json` for an Express.js API application structure.

src/Cli/StellaOps.Cli/Services/BackendOperationsClient.cs

@@ -2320,6 +2320,37 @@ internal sealed class BackendOperationsClient : IBackendOperationsClient
         return null;
     }
 
+    private static string? ExtractProblemExtensionString(ProblemDocument? problem, params string[] keys)
+    {
+        if (problem?.Extensions is null || problem.Extensions.Count == 0 || keys.Length == 0)
+        {
+            return null;
+        }
+
+        foreach (var key in keys)
+        {
+            if (!problem.Extensions.TryGetValue(key, out var value) || value is null)
+            {
+                continue;
+            }
+
+            switch (value)
+            {
+                case string text when !string.IsNullOrWhiteSpace(text):
+                    return text;
+                case JsonElement element when element.ValueKind == JsonValueKind.String:
+                    var parsed = element.GetString();
+                    if (!string.IsNullOrWhiteSpace(parsed))
+                    {
+                        return parsed;
+                    }
+                    break;
+            }
+        }
+
+        return null;
+    }
+
     private static string BuildPolicyFindingsQueryString(PolicyFindingsQuery query)
     {
         var parameters = new List<string>();
@@ -2853,6 +2884,7 @@ internal sealed class BackendOperationsClient : IBackendOperationsClient
                             {
                                 // Extract error code from problem type URI
                                 errorCode = ExtractErrorCodeFromProblemType(problem.Type);
+                                errorCode ??= ExtractProblemErrorCode(problem);
 
                                 if (!string.IsNullOrWhiteSpace(problem.Title))
                                 {
@@ -2868,21 +2900,23 @@ internal sealed class BackendOperationsClient : IBackendOperationsClient
                                 // Check for trace_id in extensions
                                 if (problem.Extensions is not null)
                                 {
-                                    if (problem.Extensions.TryGetValue("trace_id", out var tid) && tid is string tidStr)
+                                    var extensionTraceId = ExtractProblemExtensionString(problem, "trace_id", "traceId");
+                                    if (!string.IsNullOrWhiteSpace(extensionTraceId))
                                     {
-                                        traceId ??= tidStr;
+                                        traceId ??= extensionTraceId;
                                     }
-                                    if (problem.Extensions.TryGetValue("traceId", out var tid2) && tid2 is string tid2Str)
+
+                                    var extensionErrorCode = ExtractProblemExtensionString(problem, "error_code", "errorCode");
+                                    if (!string.IsNullOrWhiteSpace(extensionErrorCode))
                                     {
-                                        traceId ??= tid2Str;
+                                        errorCode ??= extensionErrorCode;
                                     }
-                                    if (problem.Extensions.TryGetValue("error_code", out var ec) && ec is string ecStr)
+
+                                    var reasonCode = ExtractProblemExtensionString(problem, "reason_code", "reasonCode");
+                                    if (!string.IsNullOrWhiteSpace(reasonCode))
                                     {
-                                        errorCode ??= ecStr;
-                                    }
-                                    if (problem.Extensions.TryGetValue("errorCode", out var ec2) && ec2 is string ec2Str)
-                                    {
-                                        errorCode ??= ec2Str;
+                                        metadata ??= new Dictionary<string, object?>(StringComparer.Ordinal);
+                                        metadata["reason_code"] = reasonCode;
                                     }
                                 }
                             }