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/JdeScoping.Core/Options/SecureStoreOptions.cs

@@ -17,17 +17,11 @@ public class SecureStoreOptions
     public string StorePath { get; set; } = "data/secrets.json";
 
     /// <summary>
-    /// Path to the key file (used in development).
+    /// Path to the key file used for encryption/decryption.
     /// Defaults to "data/secrets.key" relative to app directory.
     /// </summary>
     public string KeyFilePath { get; set; } = "data/secrets.key";
 
-    /// <summary>
-    /// Environment variable name containing the master key (used in production).
-    /// If set and the env var exists, it takes precedence over the key file.
-    /// </summary>
-    public string MasterKeyEnvVar { get; set; } = "SCOPINGTOOL_MASTER_KEY";
-
     /// <summary>
     /// Whether to auto-create the store and generate a key file on first run.
     /// </summary>