feat(attendance): 'Chybějící hodiny' (manko) row — real hours below the fond

manko = max(0, fond − (worked_total + dovolená + nemoc + neplacené volno))
using REAL clock time, not the paušál. Supplement next to Přesčas — the
verified binding formulas are untouched.

Why: the paušál Odpracováno can nominally cover the fond while dozens of
real hours are missing (Dominik 6/2026: 21 days × 8 + 8h dovolená = 176 =
fond exactly, thanks to weekend shifts compensating 3 recordless weekdays —
yet real worked time was 136,5h). Přesčas = 0 correctly, and the 31,5h gap
vanished from every total. Now it's a permanent summary line, red+bold when
positive, plus a 'Chybí: Xh' chip on the admin screen cards.

+4 tests incl. the real June dataset as a pinned acceptance case (also
pins noc 6,75 — early shifts starting 05:30/05:45 legitimately count
night minutes before 06:00).

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

src/admin/hooks/useAttendanceAdmin.ts

@@ -97,6 +97,7 @@ interface UserTotal {
   weekend_hours?: number;
   night_minutes?: number;
   worked_holiday_hours?: number; // sum of hours worked ON a holiday
+  manko?: number; // Chybějící hodiny: real clock time below the fond
   records?: AttendanceRecord[];
 }
 
@@ -243,6 +244,7 @@ function computeUserTotals(
     t.weekend_hours = s.weekendHours;
     t.night_minutes = s.nightMinutes;
     t.worked_holiday_hours = s.svatekHours;
+    t.manko = s.manko;
   }
 
   return totals;
@@ -427,6 +429,10 @@ export function buildUserSectionHtml(
       <span class="summary-label">Přesčas:</span>
       <span class="summary-value">${formatHoursDecimal(s.prescas * 60)}h</span>
     </div>
+    <div class="summary-row${s.manko > 0 ? " summary-alert" : ""}">
+      <span class="summary-label">Chybějící hodiny:</span>
+      <span class="summary-value">${formatHoursDecimal(s.manko * 60)}h</span>
+    </div>
     <div class="summary-row">
       <span class="summary-label">Svátek:</span>
       <span class="summary-value">${formatHoursDecimal(s.svatekHours * 60)}h</span>
@@ -547,6 +553,9 @@ export function buildPrintHtml(
     }
     .user-summary .summary-label { color: #555; }
     .user-summary .summary-value { font-weight: 600; }
+    /* Chybějící hodiny > 0 — must jump out of the sheet, not hide in it. */
+    .user-summary .summary-alert .summary-label,
+    .user-summary .summary-alert .summary-value { color: #b00020; font-weight: 700; }
     .user-summary .summary-fund {
       border-top: 1px solid #ddd; margin-top: 4px; padding-top: 6px;
     }