refactor(securestore): store entire connection strings in SecureStore

Eliminates placeholder substitution (${KEY}) in favor of storing complete
connection strings as single encrypted values. SecureStore now auto-creates
entries for all connection strings defined in appsettings. ConfigManager
editor reads/writes values directly to SecureStore.

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

@@ -31,4 +31,10 @@ public class SecureStoreOptions
     /// List of secret keys that must exist in the store for the application to start.
     /// </summary>
     public List<string> RequiredKeys { get; set; } = [];
+
+    /// <summary>
+    /// List of connection string names that must exist in the store.
+    /// Populated automatically from the ConnectionStrings configuration section.
+    /// </summary>
+    public List<string> RequiredConnectionStrings { get; set; } = [];
 }