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/routes/admin/dashboard.ts

@@ -3,6 +3,7 @@ import prisma from "../../config/database";
 import { requireAuth } from "../../middleware/auth";
 import { success } from "../../utils/response";
 import { localTimeStr } from "../../utils/date";
+import { toCzk } from "../../services/exchange-rates";
 
 export default async function dashboardRoutes(
   fastify: FastifyInstance,
@@ -206,10 +207,13 @@ export default async function dashboardRoutes(
           }),
         ),
         unpaid_count: unpaidCount,
-        revenue_czk:
-          revenueByCurrency["CZK"] != null
-            ? Math.round(revenueByCurrency["CZK"] * 100) / 100
-            : null,
+        revenue_czk: await (async () => {
+          let total = 0;
+          for (const [cur, amount] of Object.entries(revenueByCurrency)) {
+            total += await toCzk(Math.round(amount * 100) / 100, cur);
+          }
+          return Math.round(total * 100) / 100;
+        })(),
       };
       result.unpaid_invoices = unpaidCount;
     }