feat: CNB exchange rates, multi-currency KPI stats, invoice PDF VAT in CZK

- ČNB exchange rate service with date-specific rates and caching
- Invoice/received invoice stats convert foreign currencies to CZK
- Dashboard revenue converts all currencies to CZK
- Invoice PDF: VAT recap table always in CZK with CNB rate footer
- Inline styles replaced with utility classes (step 4 cleanup)
- Spinner animation exempt from prefers-reduced-motion

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/exchange-rates.ts

@@ -0,0 +1,65 @@
+/**
+ * Czech National Bank (ČNB) exchange rate service.
+ * Fetches daily rates and caches them.
+ * API: https://api.cnb.cz/cnbapi/exrates/daily
+ */
+
+interface CnbRate {
+  currencyCode: string;
+  rate: number;
+  amount: number;
+}
+
+const rateCache: Record<string, Record<string, number>> = {};
+
+async function fetchRatesForDate(
+  date?: string,
+): Promise<Record<string, number>> {
+  const key = date || "today";
+  if (rateCache[key]) return rateCache[key];
+
+  try {
+    let url = "https://api.cnb.cz/cnbapi/exrates/daily?lang=EN";
+    if (date) url += `&date=${date}`;
+
+    const response = await fetch(url);
+    if (!response.ok) throw new Error(`CNB API: ${response.status}`);
+
+    const data = (await response.json()) as { rates: CnbRate[] };
+    const rates: Record<string, number> = { CZK: 1 };
+
+    for (const r of data.rates) {
+      rates[r.currencyCode] = r.rate / r.amount;
+    }
+
+    rateCache[key] = rates;
+    return rates;
+  } catch (err) {
+    console.error("Failed to fetch CNB exchange rates:", err);
+    if (rateCache["today"]) return rateCache["today"];
+    return { CZK: 1, EUR: 25, USD: 22, GBP: 28 };
+  }
+}
+
+/** Convert an amount from a given currency to CZK using CNB rates */
+export async function toCzk(
+  amount: number,
+  currency: string,
+  date?: string,
+): Promise<number> {
+  if (currency === "CZK") return amount;
+  const rates = await fetchRatesForDate(date);
+  const rate = rates[currency];
+  if (!rate) return amount;
+  return Math.round(amount * rate * 100) / 100;
+}
+
+/** Get CNB rate for a currency (CZK per 1 unit), optionally for a specific date */
+export async function getRate(
+  currency: string,
+  date?: string,
+): Promise<number> {
+  if (currency === "CZK") return 1;
+  const rates = await fetchRatesForDate(date);
+  return rates[currency] || 1;
+}

src/services/invoices.service.ts

@@ -1,4 +1,5 @@
 import prisma from "../config/database";
+import { toCzk } from "./exchange-rates";
 
 // Status transition rules matching PHP
 const VALID_TRANSITIONS: Record<string, string[]> = {
@@ -186,10 +187,11 @@ export async function getInvoiceStats(queryMonth?: number, queryYear?: number) {
       }));
   };
 
-  const sumCzk = (invoices: typeof allInvoices) => {
+  const sumCzk = async (invoices: typeof allInvoices) => {
     let total = 0;
     for (const inv of invoices) {
-      total += invoiceTotalWithVat(inv); // Simplified: no real FX conversion
+      const amount = invoiceTotalWithVat(inv);
+      total += await toCzk(amount, inv.currency || "CZK");
     }
     return Math.round(total * 100) / 100;
   };
@@ -224,18 +226,24 @@ export async function getInvoiceStats(queryMonth?: number, queryYear?: number) {
   let vatCzk = 0;
   for (const [, v] of Object.entries(vatMap)) vatCzk += v;
 
+  // VAT also needs conversion
+  let vatCzkConverted = 0;
+  for (const [cur, amount] of Object.entries(vatMap)) {
+    vatCzkConverted += await toCzk(amount, cur);
+  }
+
   return {
     paid_month: aggregateByCurrency(paidInvoices),
-    paid_month_czk: sumCzk(paidInvoices),
+    paid_month_czk: await sumCzk(paidInvoices),
     paid_month_count: paidInvoices.length,
     awaiting: aggregateByCurrency(awaitingInvoices),
-    awaiting_czk: sumCzk(awaitingInvoices),
+    awaiting_czk: await sumCzk(awaitingInvoices),
     awaiting_count: awaitingInvoices.length,
     overdue: aggregateByCurrency(overdueInvoices),
-    overdue_czk: sumCzk(overdueInvoices),
+    overdue_czk: await sumCzk(overdueInvoices),
     overdue_count: overdueInvoices.length,
     vat_month: vatAmounts,
-    vat_month_czk: Math.round(vatCzk * 100) / 100,
+    vat_month_czk: Math.round(vatCzkConverted * 100) / 100,
     month,
     year,
   };