fix(holidays): honest dates and reachable fields on the holidays page

The table had two date columns for one date: "تاریخ" printed the raw
1405-05-13 string in Latin digits, and the column labelled "میلادی" ran the
same day through formatDate — which returns Jalali. One date, twice, under a
label that lied. It is now a single formatted Jalali column.

The closure form used a native <input type="date">: Gregorian, an English
mm/dd/yyyy placeholder in an RTL Persian panel, and a white box in dark mode
because a native control does not follow the theme. It is the shared Persian
picker now.

That picker turned out to be a div with an onClick — no role, no tab stop, no
accessible name, and its clear button was a span. Since every page that picks
a date goes through it, it gained role/tabIndex/Enter-Space, an ariaLabel
prop, and a real button for clear. The page passes labels for the year select
and both form fields, and the global topbar search got an aria-label, which
takes the runtime accessibility probe on this page to clean.

useHolidays now returns an error, so a failed request reads as an error
instead of an empty year — previously indistinguishable.

The page had no test file; it has eight.

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

assets/admin/hooks/useResourceCalendar.ts

@@ -106,6 +106,9 @@ export function useHolidays(year: number) {
     holidays: query.data?.data?.holidays ?? [],
     overrides: query.data?.data?.overrides ?? [],
     loading: query.isLoading,
+    // بدون این، درخواستِ شکست‌خورده مثل «سالِ خالی» دیده می‌شود و کاربر دنبال
+    // تعطیلاتی می‌گردد که ثبت شده‌اند ولی نیامده‌اند.
+    error: query.isError ? ((query.error as Error)?.message || 'خطای نامشخص') : null,
     setOverride,
     removeOverride,
   };