refactor(securestore): remove password-based authentication in favor of key-file only

Simplify SecureStore by removing MasterKeyEnvVar and password-based methods, leaving only key-file authentication for better security practices.

NEW/src/Utils/JdeScoping.ConfigManager/Models/ConfigModel.cs

@@ -252,15 +252,10 @@ public class SecureStoreSection
     public string StorePath { get; set; } = "data/secrets.json";
 
     /// <summary>
-    /// Gets or sets the path to the key file for decryption.
+    /// Gets or sets the path to the key file for encryption/decryption.
     /// </summary>
     public string KeyFilePath { get; set; } = "data/secrets.key";
 
-    /// <summary>
-    /// Gets or sets the environment variable name for the master key.
-    /// </summary>
-    public string MasterKeyEnvVar { get; set; } = "SCOPINGTOOL_MASTER_KEY";
-
     /// <summary>
     /// Gets or sets a value indicating whether to auto-create the store if it doesn't exist.
     /// </summary>