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/admin/pages/ReceivedInvoices.tsx

@@ -115,7 +115,7 @@ function formatCzkWithDetail(
     return { value: "0 Kč", detail: null };
   }
   const hasForeign = amounts.some((a) => a.currency !== "CZK");
-  if (hasForeign && totalCzk !== null && totalCzk !== undefined) {
+  if (hasForeign && totalCzk != null) {
     return {
       value: formatCurrency(totalCzk, "CZK"),
       detail: formatMultiCurrency(amounts),
@@ -709,9 +709,9 @@ export default function ReceivedInvoices({
               <p>Žádné přijaté faktury v tomto měsíci.</p>
               {hasPermission("invoices.create") && (
                 <p
+                  className="text-md"
                   style={{
                     color: "var(--text-tertiary)",
-                    fontSize: "0.875rem",
                   }}
                 >
                   Nahrajte faktury tlačítkem výše.
@@ -780,7 +780,8 @@ export default function ReceivedInvoices({
                       />
                     </th>
                     <th
-                      style={{ textAlign: "right", cursor: "pointer" }}
+                      className="text-right"
+                      style={{ cursor: "pointer" }}
                       onClick={() => handleSort("amount")}
                     >
                       Částka{" "}
@@ -959,9 +960,9 @@ export default function ReceivedInvoices({
                     Vybrat soubory
                   </button>
                   <span
+                    className="text-sm"
                     style={{
                       marginLeft: "0.75rem",
-                      fontSize: "0.8125rem",
                       color: "var(--text-tertiary)",
                     }}
                   >
@@ -1106,8 +1107,8 @@ export default function ReceivedInvoices({
                         </div>
                         {uploadMeta[idx]?.amount && (
                           <div
+                            className="text-xs"
                             style={{
-                              fontSize: "0.75rem",
                               color: "var(--text-tertiary)",
                               marginTop: "-0.25rem",
                               marginBottom: "0.5rem",
@@ -1320,8 +1321,8 @@ export default function ReceivedInvoices({
                         </div>
                         {editInvoice.amount && (
                           <div
+                            className="text-xs"
                             style={{
-                              fontSize: "0.75rem",
                               color: "var(--text-tertiary)",
                               marginBottom: "0.75rem",
                             }}