Add Go configuration model

internal/core/config/redaction.go

@@ -0,0 +1,17 @@
+package config
+
+const redactedSecret = "[REDACTED]"
+
+func (c Config) Redacted() Config {
+	redacted := c
+	redacted.PrimaryLLM.APIKey = redactSecret(redacted.PrimaryLLM.APIKey)
+	redacted.ValidationLLM.APIKey = redactSecret(redacted.ValidationLLM.APIKey)
+	return redacted
+}
+
+func redactSecret(value string) string {
+	if value == "" {
+		return ""
+	}
+	return redactedSecret
+}