feat(csms): add system settings management for OCPP 1.6J heartbeat interval

apps/web/lib/api.ts

@@ -202,6 +202,14 @@ export type TariffConfig = {
   updatedAt?: string;
 };
 
+export type Ocpp16jSettings = {
+  heartbeatInterval: number;
+};
+
+export type SystemSettings = {
+  ocpp16j: Ocpp16jSettings;
+};
+
 // ── API functions ──────────────────────────────────────────────────────────
 
 export type ChartRange = "30d" | "7d" | "24h";
@@ -349,4 +357,9 @@ export const api = {
     put: (data: { slots: TariffSlot[]; prices: Record<PriceTier, TierPricing> }) =>
       apiFetch<TariffConfig>("/api/tariff", { method: "PUT", body: JSON.stringify(data) }),
   },
+  settings: {
+    get: () => apiFetch<SystemSettings>("/api/settings"),
+    put: (data: SystemSettings) =>
+      apiFetch<SystemSettings>("/api/settings", { method: "PUT", body: JSON.stringify(data) }),
+  },
 };