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/Offers.tsx

@@ -814,8 +814,8 @@ export default function Offers() {
                     <tr>
                       <td
                         colSpan={8}
-                        className="text-muted"
-                        style={{ textAlign: "center", padding: "1.5rem" }}
+                        className="text-muted text-center"
+                        style={{ padding: "1.5rem" }}
                       >
                         Žádné nabídky odpovídající hledání.
                       </td>
@@ -879,8 +879,8 @@ export default function Offers() {
               <div className="admin-modal-header">
                 <h2 className="admin-modal-title">Vytvořit objednávku</h2>
                 <p
-                  className="text-secondary"
-                  style={{ marginTop: "0.25rem", fontSize: "0.875rem" }}
+                  className="text-secondary text-md"
+                  style={{ marginTop: "0.25rem" }}
                 >
                   Nabídka:{" "}
                   <strong>{orderModal.quotation?.quotation_number}</strong>
@@ -917,7 +917,7 @@ export default function Offers() {
                           <path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z" />
                           <polyline points="14 2 14 8 20 8" />
                         </svg>
-                        <span style={{ fontSize: "0.875rem" }}>
+                        <span className="text-md">
                           {orderAttachment.name}{" "}
                           <span className="text-tertiary">
                             ({(orderAttachment.size / 1024).toFixed(0)} KB)
@@ -944,11 +944,9 @@ export default function Offers() {
                       </div>
                     ) : (
                       <label
-                        className="admin-btn admin-btn-secondary admin-btn-sm"
+                        className="admin-btn admin-btn-secondary admin-btn-sm inline-flex"
                         style={{
                           cursor: "pointer",
-                          display: "inline-flex",
-                          alignItems: "center",
                           gap: "0.4rem",
                         }}
                       >