security: fix all Medium findings from FLAWS_REPORT audit

- Auth: TOTP replay protection with counter tracking, constant-time
  backup code comparison, atomic lockout increment, per-token logout
- Invoices/PDFs: net-based VAT calculation, dangerous URL scheme
  stripping in cleanQuillHtml, orders-pdf error handling
- Orders: reject item changes on status transition, cascading
  delete cleanup, take:1 with orderBy
- Projects: atomic rename collision handling, MIME/extension
  validation, empty customer name rejection
- Attendance: Czech public holiday awareness in frontend fund
  calculation, leave_hours 0 handling, invalid date NaN guard,
  bounded per-month queries in workfund
- Users/Admin: profile audit logging + password validation, session
  revocation guard, session ID validation, dashboard DB aggregation,
  soft-deleted record protection in scope templates
- Frontend: FormField label linkage, Pagination ARIA, error
  handling in OrderConfirmationModal, 401 propagation, GPS emoji
  hidden from screen readers, table sort state fix, geolocation
  race/abort cleanup, Leaflet popup DOM safety, Vehicles toggleActive
  minimal body, CompanySettings ref mutation fix, OfferDetail unlock
  abort, AttendanceBalances combined fetches
- Utils: env validation, Puppeteer concurrency mutex, invoice alert
  cron cleanup on shutdown, body limit alignment, TOTP error logging,
  trustProxy from env, symlink rejection, rate cache Map usage

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/services/exchange-rates.ts

@@ -10,13 +10,13 @@ interface CnbRate {
   amount: number;
 }
 
-const rateCache: Record<string, Record<string, number>> = {};
+const rateCache = new Map<string, Record<string, number>>();
 
 async function fetchRatesForDate(
   date?: string,
 ): Promise<Record<string, number>> {
   const key = date || "today";
-  if (rateCache[key]) return rateCache[key];
+  if (rateCache.has(key)) return rateCache.get(key)!;
 
   try {
     let url = "https://api.cnb.cz/cnbapi/exrates/daily?lang=EN";
@@ -32,11 +32,11 @@ async function fetchRatesForDate(
       rates[r.currencyCode] = r.rate / r.amount;
     }
 
-    rateCache[key] = rates;
+    rateCache.set(key, rates);
     return rates;
   } catch (err) {
     console.error("Failed to fetch CNB exchange rates:", err);
-    if (rateCache["today"]) return rateCache["today"];
+    if (rateCache.has("today")) return rateCache.get("today")!;
     throw new Error("Nepodařilo se získat aktuální kurzy z ČNB");
   }
 }