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/routes/admin/received-invoices.ts

@@ -263,10 +263,10 @@ export default async function receivedInvoicesRoutes(
           const meta = invoicesMeta[i] || {};
           const amount = Number(meta.amount ?? 0);
           const vatRate = Number(meta.vat_rate ?? 21);
-          // Amount includes VAT — extract VAT portion: amount - amount/(1 + rate/100)
+          // Amount is net — VAT = amount * rate / 100
           const vatAmount =
             vatRate > 0
-              ? Math.round((amount - amount / (1 + vatRate / 100)) * 100) / 100
+              ? Math.round(((amount * vatRate) / 100) * 100) / 100
               : 0;
 
           const issueDate = meta.issue_date
@@ -434,13 +434,9 @@ export default async function receivedInvoicesRoutes(
         body.vat_rate !== undefined
           ? Number(body.vat_rate)
           : Number(existing.vat_rate);
-      // Amount includes VAT — extract VAT portion: amount - amount/(1 + rate/100)
+      // Amount is net — VAT = amount * rate / 100
       const computedVat =
-        finalVatRate > 0
-          ? roundMoney(
-              finalAmount - roundMoney(finalAmount / (1 + finalVatRate / 100)),
-            )
-          : 0;
+        finalVatRate > 0 ? roundMoney((finalAmount * finalVatRate) / 100) : 0;
 
       // Auto-set paid_date when status transitions to paid (matching PHP)
       const newStatus =