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/components/layout/Topbar.tsx

@@ -38,7 +38,7 @@ export default function Topbar({ onMobileMenuOpen }: { onMobileMenuOpen?: () =>
         {/* Search bar — placeholder «جستجو» مطابق clinic-pro-tauri */}
         <div className="topbar-search">
           <MagnifyingGlassIcon style={{ width: 17, height: 17, flexShrink: 0 }} />
-          <input placeholder="جستجو" readOnly />
+          <input placeholder="جستجو" aria-label="جستجو" readOnly />
         </div>
 
         <div style={{ flex: 1 }} />