feat: add startup config validation and document ConfigManager pipeline editor

Add ConfigurationValidationRunner with IConfigurationValidator interface for
validating required settings at startup. Includes SecureStore and LDAP validators.
Expand ConfigManager with pipeline editing UI, dialogs, and step editors.
Update documentation with config validation guidance.

NEW/src/JdeScoping.Core/Options/SecureStoreOptions.cs

@@ -34,7 +34,7 @@ public class SecureStoreOptions
     public bool AutoCreateStore { get; set; } = true;
 
     /// <summary>
-    /// Whether to migrate existing secrets (RSA key, Excel passwords) on startup.
+    /// List of secret keys that must exist in the store for the application to start.
     /// </summary>
-    public bool MigrateExistingSecrets { get; set; } = true;
+    public List<string> RequiredKeys { get; set; } = [];
 }