fix(attendance): timezone-proof print dates; overnight-only time prefixes

Two bugs in the attendance admin print (Tisk on Správa docházky):

1. Viewer-timezone date shift: day rows are built from date-only strings
   ('2026-06-01'), which new Date() parses as UTC midnight per spec; local
   formatting then rendered the PREVIOUS day for any viewer west of UTC —
   a June print opened with '31. 5. Neděle' (a May row holding June 1's
   punches) and every weekday name + weekend tint shifted by one. Czech
   viewers were unaffected (UTC+1/+2), US viewers always hit it.
   formatDate / getCzechWeekday / isWeekendDate now parse the calendar day
   from the string parts — identical output in every timezone.

2. Every time cell carried a bogus date prefix ('1.6. 08:00'): the
   overnight-only guard compared the extracted date part against the raw
   wire shift_date ('2026-06-01T02:00:00') — never equal. Now compares
   normalized date parts; the prefix fires only for true overnight punches.

Verified end-to-end against the production June payload; +8 regression
tests (timezone-proof by construction — parts-based, no UTC parse).

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

src/admin/utils/attendanceHelpers.ts

@@ -173,7 +173,10 @@ export const formatTimeOrDatetimePrint = (
   const timeDate = dateMatch
     ? `${dateMatch[1]}-${dateMatch[2]}-${dateMatch[3]}`
     : "";
-  if (timeDate && timeDate !== shiftDate) {
+  // Compare DATE PARTS: shiftDate arrives as a naive datetime off the wire
+  // ("2026-06-01T02:00:00"), so a raw string compare never matched and the
+  // overnight-only date prefix fired on every single time cell.
+  if (timeDate && timeDate !== normalizeDateStr(shiftDate)) {
     const datePart = `${parseInt(dateMatch![3])}.${parseInt(dateMatch![2])}.`;
     return `${datePart} ${extractTime(datetime)}`;
   }
@@ -203,9 +206,23 @@ export const calculateWorkMinutesPrint = (record: AttendanceRecord): number => {
 // Print template helpers (mzda-style counting)
 // ---------------------------------------------------------------------------
 
+/**
+ * Parse the calendar day of a date-only or naive-datetime string as a LOCAL
+ * Date. `new Date("YYYY-MM-DD")` is UTC midnight per the ECMAScript spec —
+ * in timezones west of UTC it renders as the PREVIOUS day, so a US viewer's
+ * June print started with "31. 5. Neděle" and every weekday name was shifted.
+ * Building the Date from its string parts keeps the calendar day identical
+ * in every timezone.
+ */
+const localDayFromString = (dateStr: string): Date => {
+  const m = String(dateStr).match(/^(\d{4})-(\d{2})-(\d{2})/);
+  if (m) return new Date(Number(m[1]), Number(m[2]) - 1, Number(m[3]));
+  return new Date(dateStr);
+};
+
 /** Returns the Czech weekday name with the first letter capitalized. */
 export const getCzechWeekday = (dateStr: string): string => {
-  const wd = new Date(dateStr).toLocaleDateString("cs-CZ", {
+  const wd = localDayFromString(dateStr).toLocaleDateString("cs-CZ", {
     weekday: "long",
   });
   return wd.charAt(0).toUpperCase() + wd.slice(1);
@@ -213,7 +230,7 @@ export const getCzechWeekday = (dateStr: string): string => {
 
 /** True if the date is a Saturday or Sunday. */
 export const isWeekendDate = (dateStr: string): boolean => {
-  const dow = new Date(dateStr).getDay();
+  const dow = localDayFromString(dateStr).getDay();
   return dow === 0 || dow === 6;
 };
 

src/admin/utils/formatters.ts

@@ -33,7 +33,15 @@ export function formatMultiCurrency(
 
 export function formatDate(dateStr: string | null | undefined): string {
   if (!dateStr) return "—";
-  const d = new Date(dateStr);
+  // Date-ONLY strings ("2026-06-01") parse as UTC midnight per the spec, which
+  // renders as the PREVIOUS day in timezones west of UTC — a US viewer's June
+  // attendance print started with 31. 5. Parse the parts instead so the
+  // calendar day is identical in every timezone. Datetime strings keep the
+  // local-parse behavior (naive wire times are already local).
+  const m = String(dateStr).match(/^(\d{4})-(\d{2})-(\d{2})$/);
+  const d = m
+    ? new Date(Number(m[1]), Number(m[2]) - 1, Number(m[3]))
+    : new Date(dateStr);
   return d.toLocaleDateString("cs-CZ");
 }