Feature: System settings in DB - configurable backend URLs and API key

backend/db/postgres.go

@@ -216,6 +216,17 @@ func (d *Database) migrate() error {
 	)`)
 	d.db.Exec(`CREATE INDEX IF NOT EXISTS idx_audit_log_timestamp ON audit_log(timestamp DESC)`)
 
+	// System Settings Tabelle
+	d.db.Exec(`CREATE TABLE IF NOT EXISTS system_settings (
+		key TEXT PRIMARY KEY,
+		value TEXT NOT NULL,
+		updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+	)`)
+	// Default-Keys anlegen (leere Werte)
+	for _, k := range []string{"backend_url_internal", "backend_url_external", "api_key"} {
+		d.db.Exec(`INSERT INTO system_settings (key, value) VALUES ($1, '') ON CONFLICT DO NOTHING`, k)
+	}
+
 	// Retention Policy (90 Tage)
 	d.setupRetention()
 
@@ -1197,6 +1208,42 @@ func (d *Database) GetAuditLogs(limit int, offset int, action string, agentID st
 	return entries, total, rows.Err()
 }
 
+// --- System Settings ---
+
+func (d *Database) GetSettings() (map[string]string, error) {
+	rows, err := d.db.Query("SELECT key, value FROM system_settings ORDER BY key")
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	settings := make(map[string]string)
+	for rows.Next() {
+		var k, v string
+		if err := rows.Scan(&k, &v); err != nil {
+			return nil, err
+		}
+		settings[k] = v
+	}
+	return settings, rows.Err()
+}
+
+func (d *Database) GetSetting(key string) (string, error) {
+	var value string
+	err := d.db.QueryRow("SELECT value FROM system_settings WHERE key = $1", key).Scan(&value)
+	if err != nil {
+		return "", err
+	}
+	return value, nil
+}
+
+func (d *Database) SetSetting(key, value string) error {
+	_, err := d.db.Exec(`
+		INSERT INTO system_settings (key, value, updated_at) VALUES ($1, $2, NOW())
+		ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value, updated_at = NOW()
+	`, key, value)
+	return err
+}
+
 func (d *Database) MigrateConfigAPIKeys(configKeys []string) {
 	for _, key := range configKeys {
 		var exists bool