Fix VIRTUAL_ENV not set during ComfyUI-Zluda installation

The install-sm.bat script requires VIRTUAL_ENV to be set for ZLUDA DLL
patching to work correctly. Without this, the DLL copy commands fail
silently, leaving original NVIDIA libraries unchanged and causing
cublas errors during generation.

This fix adds VIRTUAL_ENV=venv to the environment variables passed
to the installation batch script.

Author: NeuralFault

StabilityMatrix.Core/Models/Packages/ComfyZluda.cs

@@ -109,7 +109,7 @@ await newInstallBatPath
             [],
             installLocation,
             onConsoleOutput,
-            GetEnvVars(true)
+            GetEnvVars(true, installLocation)
         );
         await installProcess.WaitForExitAsync(cancellationToken).ConfigureAwait(false);
 
@@ -141,7 +141,7 @@ await SetupVenv(installLocation, pythonVersion: PyVersion.Parse(installedPackage
             args,
             installLocation,
             HandleConsoleOutput,
-            GetEnvVars(false)
+            GetEnvVars(false, installLocation)
         );
 
         return;
@@ -184,7 +184,7 @@ await zludaProcess
         GC.SuppressFinalize(this);
     }
 
-    private Dictionary<string, string> GetEnvVars(bool isInstall)
+    private Dictionary<string, string> GetEnvVars(bool isInstall, string installLocation)
     {
         var portableGitBin = new DirectoryPath(PrerequisiteHelper.GitBinPath);
         var hipPath = Path.Combine(
@@ -202,6 +202,11 @@ private Dictionary<string, string> GetEnvVars(bool isInstall)
             ["GIT"] = portableGitBin.JoinFile("git.exe"),
         };
 
+        if (isInstall)
+        {
+            envVars["VIRTUAL_ENV"] = "venv";
+        }
+
         if (envVars.TryGetValue("PATH", out var pathValue))
         {
             envVars["PATH"] = Compat.GetEnvPathWithExtensions(hipBinPath, portableGitBin, pathValue);