feat(frontend): add test deps, VAT types, and business info store

Add jsdom and vitest dev dependencies. Add total_vat_amount and total_net_amount to PaymentSummary type. Create shared businessInfo store for caching public business settings.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/src/lib/stores/businessInfo.svelte.ts

@@ -0,0 +1,36 @@
+// src/lib/stores/businessInfo.svelte.ts
+import type { BusinessSettings } from '$lib/types/settings';
+
+let businessInfo = $state<BusinessSettings | null>(null);
+let loadingPromise: Promise<BusinessSettings | null> | null = null;
+
+/**
+ * Fetches /api/business-info exactly once and caches the result.
+ * Subsequent calls return the cached promise or resolved value.
+ * Errors are handled gracefully — returns null.
+ */
+export async function ensureBusinessInfo(): Promise<BusinessSettings | null> {
+	if (businessInfo !== null) return businessInfo;
+	if (loadingPromise) return loadingPromise;
+
+	loadingPromise = fetch('/api/business-info')
+		.then((r) => (r.ok ? r.json() : null))
+		.then((data) => {
+			businessInfo = data as BusinessSettings | null;
+			return businessInfo;
+		})
+		.catch(() => {
+			businessInfo = null;
+			return null;
+		});
+
+	return loadingPromise;
+}
+
+/**
+ * Returns the current cached business info (reactive via $state).
+ * Use in $derived or $effect to track changes.
+ */
+export function getBusinessInfo(): BusinessSettings | null {
+	return businessInfo;
+}

frontend/src/lib/types/index.ts

@@ -48,6 +48,8 @@ export interface PaymentSummary {
 	paid_amount: number;
 	refunded_amount: number;
 	remaining_amount: number;
+	total_vat_amount: number;
+	total_net_amount: number;
 	payments: Payment[];
 	refunds: Refund[];
 }