[WI1] Address code review feedback - extract magic strings to constants

- Add TargetFramework constant ("net9.0") for maintainability
- Add AppHostAssemblyName constant for assembly DLL name
- Replace hardcoded strings in DetermineBuildConfiguration()
- Improves future .NET version updates
- Complete WI1 documentation with lessons learned

Co-authored-by: devstress <30769729+devstress@users.noreply.github.com>

Author: Copilot

LearningCourse/LearningCourse.IntegrationTests/LearningCourseTestBase.cs

@@ -24,6 +24,10 @@ public abstract class LearningCourseTestBase
         "LocalTesting", "LocalTesting.FlinkSqlAppHost");
     private static StreamWriter? _debugLogWriter;
 
+    // Build configuration constants
+    private const string TargetFramework = "net9.0";
+    private const string AppHostAssemblyName = "LocalTesting.FlinkSqlAppHost.dll";
+    
     /// <summary>
     /// Kafka container IP for Flink jobs (e.g., "172.17.0.2:9093").
     /// Docker bridge network doesn't support DNS, so we use actual IP address.
@@ -197,15 +201,15 @@ public static async Task GlobalSetUp()
     private static (bool shouldBuild, string configuration) DetermineBuildConfiguration()
     {
         // Check for Release build
-        var releaseDll = Path.Combine(AppHostPath, "bin", "Release", "net9.0", "LocalTesting.FlinkSqlAppHost.dll");
+        var releaseDll = Path.Combine(AppHostPath, "bin", "Release", TargetFramework, AppHostAssemblyName);
         if (File.Exists(releaseDll))
         {
             TestContext.WriteLine($"✅ Release build found at {releaseDll}");
             return (false, "Release");
         }
 
         // Check for Debug build
-        var debugDll = Path.Combine(AppHostPath, "bin", "Debug", "net9.0", "LocalTesting.FlinkSqlAppHost.dll");
+        var debugDll = Path.Combine(AppHostPath, "bin", "Debug", TargetFramework, AppHostAssemblyName);
         if (File.Exists(debugDll))
         {
             TestContext.WriteLine($"✅ Debug build found at {debugDll}");