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/config/env.ts

@@ -81,7 +81,41 @@ export const config = {
     origins: (process.env.CORS_ORIGINS || "").split(",").filter(Boolean),
   },
 
+  trustProxy: (process.env.TRUST_PROXY || "")
+    .split(",")
+    .map((s) => s.trim())
+    .filter(Boolean),
+
   security: {
     bcryptCost: 12,
   },
 } as const;
+
+const HEX64_RE = /^[0-9a-fA-F]{64}$/;
+if (!HEX64_RE.test(config.jwt.secret)) {
+  throw new Error("JWT_SECRET must be a 64-character hex string");
+}
+if (!HEX64_RE.test(config.totp.encryptionKey)) {
+  throw new Error("TOTP_ENCRYPTION_KEY must be a 64-character hex string");
+}
+if (Number.isNaN(config.port) || config.port < 1 || config.port > 65535) {
+  throw new Error("PORT must be a valid TCP port (1-65535)");
+}
+if (
+  Number.isNaN(config.jwt.accessTokenExpiry) ||
+  config.jwt.accessTokenExpiry <= 0
+) {
+  throw new Error("ACCESS_TOKEN_EXPIRY must be a positive integer");
+}
+if (
+  Number.isNaN(config.jwt.refreshTokenSessionExpiry) ||
+  config.jwt.refreshTokenSessionExpiry <= 0
+) {
+  throw new Error("REFRESH_TOKEN_SESSION_EXPIRY must be a positive integer");
+}
+if (
+  Number.isNaN(config.jwt.refreshTokenRememberExpiry) ||
+  config.jwt.refreshTokenRememberExpiry <= 0
+) {
+  throw new Error("REFRESH_TOKEN_REMEMBER_EXPIRY must be a positive integer");
+}