ConfigStore: default installRoot to C:\ASTERION_VR for client installs

Previous default fell back to %UserProfile%\ASTERION_VR which is
fine for dev but unconventional for end users; the standard
deployment path is plainly C:\ASTERION_VR. New first-launch behavior:

1. If a sibling ASTERION_VR exists next to the exe (portable / dev
   layout), prefer it — keeps the development workflow intact.
2. Otherwise, default to C:\ASTERION_VR. The folder is created on
   the first install (Directory.CreateDirectory in ZipInstaller
   handles non-existent parents).

Existing users with an explicit installRoot in their config.json are
unaffected — only fresh configs (or empty installRoot) hit this path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.Core/Configuration/ConfigStore.cs

@@ -65,17 +65,21 @@ public sealed class ConfigStore : IConfigStore
         File.Move(tmp, _configFile, overwrite: true);
     }
 
+    /// <summary>
+    /// Cible standard pour les déploiements clients : <c>C:\ASTERION_VR</c>.
+    /// Si un dossier ASTERION_VR existe déjà à côté de l'exe (mode dev / portable),
+    /// il est préféré pour ne pas casser l'environnement de développement.
+    /// </summary>
     private static string ResolveDefaultInstallRoot()
     {
+        // Mode dev / portable : ASTERION_VR à côté de l'exe (par ex. dans le repo)
         var exeDir = AppContext.BaseDirectory;
-        var sibling = Path.Combine(Path.GetDirectoryName(exeDir.TrimEnd(Path.DirectorySeparatorChar))!, "ASTERION_VR");
+        var sibling = Path.Combine(
+            Path.GetDirectoryName(exeDir.TrimEnd(Path.DirectorySeparatorChar))!,
+            "ASTERION_VR");
         if (Directory.Exists(sibling)) return sibling;
 
-        var dev = @"C:\ASTERION\GIT\PS_Launcher\ASTERION_VR";
-        if (Directory.Exists(dev)) return dev;
-
-        return Path.Combine(
-            Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
-            "ASTERION_VR");
+        // Cible standard pour les clients (créée au premier install si absente)
+        return @"C:\ASTERION_VR";
     }
 }