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/schemas/common.ts

@@ -111,6 +111,40 @@ export const timeString = z.preprocess(
     .regex(/^([01]\d|2[0-3]):[0-5]\d$/, "Čas musí být ve formátu HH:MM"),
 );
 
+/**
+ * Combined local datetime string "YYYY-MM-DDTHH:MM" — the wire format the
+ * attendance forms produce by joining a date input and a time input
+ * (`${date}T${time}:00`). Tolerant of a trailing seconds component (":ss" —
+ * stripped before validating), because the client appends ":00" and an edit
+ * form round-trips a value the `Date.toJSON` override serialised as
+ * "YYYY-MM-DDTHH:MM:SS". The service parses the value with `new Date(...)`
+ * as LOCAL time (Europe/Prague) — no timezone suffix is part of the format.
+ */
+export const dateTimeString = z.preprocess(
+  (v) =>
+    typeof v === "string" && /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}/.test(v)
+      ? v.slice(0, 16)
+      : v,
+  z
+    .string()
+    .regex(
+      /^\d{4}-\d{2}-\d{2}T([01]\d|2[0-3]):[0-5]\d$/,
+      "Datum a čas musí být ve formátu YYYY-MM-DD HH:MM",
+    ),
+);
+
+/**
+ * Optional-datetime variant: ""/null mean "not set" → null (the attendance
+ * forms historically submitted empty strings for unfilled time fields, and a
+ * hard reject would 400 the whole form — including leave records that have no
+ * times at all). Pair with `.optional()` at the call site for fields that may
+ * be absent entirely (absent stays `undefined`, e.g. "don't change" on update).
+ */
+export const nullableDateTimeString = z.preprocess(
+  (v) => (v === "" || v === null ? null : v),
+  z.union([z.null(), dateTimeString]),
+);
+
 /**
  * An email field that also accepts an empty string (meaning "not set"). Many
  * settings/supplier forms submit "" for un-filled optional emails; a bare