fix: audit fix pass #1 — all 19 verified HIGH findings + critical dep cleanup

Fixes every CRITICAL/HIGH finding from the 2026-06-09 full-codebase audit
(REVIEW_FINDINGS.md); each fix went through independent spec + code-quality
review. Plan and per-task log: docs/superpowers/plans/2026-06-10-audit-high-fix-pass.md

- attendance: schemas accept the combined local datetimes the forms/service
  use (new dateTimeString helpers in schemas/common.ts), breaks persist on
  create, AttendanceCreate submit rebuilt — every submit 400'd since 519edce
- 2fa: backup codes wired to /totp/backup-verify (+ remember-me parity),
  enrollment QR generated locally via qrcode (CSP-blocked external service
  also leaked the secret), dashboard shows per-user enrollment, not policy
- invoices/orders: per-line VAT survives re-saves (numberOr 0-respecting
  coercion in formatters.ts), billing_text persists on update, issued-order
  status transitions update UI gates
- trips: real pagination on all 3 pages, GET /trips/stats server aggregate
  (shared buildTripsWhere + legacy distance coalesce), vehicle_id applies on
  PUT with both-vehicle odometer recompute, print rebuilt (sync window.open,
  escaped template, server totals)
- orders api: attachment_data PDF blob excluded from all non-binary reads
- warehouse: unit field is a Select over UnitEnum, receipt attachments
  downloadable via new authenticated GET route
- downloads: shared RFC 5987 contentDisposition helper — Czech filenames no
  longer 500 (warehouse, received-invoices, orders endpoints)
- misc: block-env hook actually blocks (exit 2 + stderr), project create
  works with empty dates, NaN filter guards on trips endpoints
- deps: remove unused concurrently (clears both critical advisories), pin
  @hono/node-server >=1.19.13 via overrides (clears the 3 moderates without
  the Prisma 6 downgrade), drop deprecated @types stubs

Gates: tsc -b clean - vitest 30 files / 342 tests (31 new) - eslint 0 errors
- build OK

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/utils/formatters.ts

@@ -50,6 +50,18 @@ export function todayLocalStr(): string {
   return `${d.getFullYear()}-${m}-${day}`;
 }
 
+/**
+ * Coerce a server-returned numeric (number | decimal-string | null/undefined)
+ * to a number, falling back ONLY when the value is missing or not numeric —
+ * NEVER on a legitimate 0 (e.g. a 0% VAT rate / reverse charge). The
+ * `Number(x) || fallback` idiom silently turns stored zeros into the fallback.
+ */
+export function numberOr(raw: unknown, fallback: number): number {
+  if (raw == null || raw === "") return fallback;
+  const n = Number(raw);
+  return Number.isFinite(n) ? n : fallback;
+}
+
 export function formatKm(km: number | string): string {
   return new Intl.NumberFormat("cs-CZ").format(Number(km) || 0);
 }