fix(dates): block past-date selection in appointment + clinic holiday pickers

Bug 556 triggered a broader audit of every date input in the app:

 - appointment-form DatePicker now has minValue=today(getLocalTimeZone()) —
   can't book or reschedule into the past (tightens bug 555 at the
   input layer too; the past-slot filter in masterdata service still
   handles the hour-granularity)
 - clinic-form holiday date picker gets the same — can't observe a
   holiday that already passed

Audit complete:
 - enquiry-form follow-up date: already had min=today (bug 556 fix)
 - appointment-form: fixed here
 - clinic-form holidays: fixed here
 - my-performance date filter: past valid (reports over history)
 - campaign-edit start/end: past valid (historical campaigns)

src/components/forms/clinic-form.tsx

@@ -399,6 +399,9 @@ export const ClinicForm = ({ value, onChange }: ClinicFormProps) => {
                                 onChange={(dv: DateValue | null) =>
                                     updateHoliday(idx, { date: dv ? dv.toString() : '' })
                                 }
+                                // Holidays must be today or in the future — you
+                                // can't observe a holiday that already passed.
+                                minValue={today(getLocalTimeZone())}
                             />
                         </div>
                         <div className="flex-1">