fix(agenda): fix $.map crash and getPacientes type mismatch; restore preloader

AgendaView:
- Fix agendamentos?.filter(...).map(...) crash: optional chain didn't guard .map when agendamentos is null on initial render
- Fix getPacientes fetcher to extract .data array — API now returns {data, total} not Paciente[], causing searchResults.map crash

LoginView:
- Restore 3s preloader splash screen with {APP_VERSION} instead of hardcoded version string

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/views/AgendaView.tsx

@@ -44,7 +44,7 @@ const AppointmentModal: React.FC<{
 
     const debouncedSearchTerm = useDebounce(searchTerm, 400);
 
-    const fetcher = useCallback(() => HybridBackend.getPacientes(debouncedSearchTerm), [debouncedSearchTerm]);
+    const fetcher = useCallback(() => HybridBackend.getPacientes(debouncedSearchTerm).then(r => Array.isArray(r.data) ? r.data : []), [debouncedSearchTerm]);
     const { data: searchResults, isLoading: isSearching } = useHybridBackend<Paciente[]>(fetcher, [debouncedSearchTerm]);
 
     const { data: agendamentos, refresh: refreshAgendamentos } = useHybridBackend<Agendamento[]>(HybridBackend.getAgendamentos);
@@ -93,14 +93,14 @@ const AppointmentModal: React.FC<{
         const slots: string[] = [];
         if (!selectedDentistId || !selectedDate) return slots;
 
-        const existingAppointments = agendamentos?.filter(ag =>
+        const existingAppointments = (agendamentos ?? []).filter(ag =>
             ag.dentistaId === selectedDentistId &&
             new Date(ag.start).toISOString().split('T')[0] === selectedDate &&
             ag.id !== initialAppointment?.id
         ).map(ag => ({
             start: new Date(ag.start).getHours() * 60 + new Date(ag.start).getMinutes(),
             end: new Date(ag.end).getHours() * 60 + new Date(ag.end).getMinutes(),
-        })) || [];
+        }));
 
         const dayOfWeek = new Date(selectedDate).getUTCDay();
         const dayHorarios = allHorarios?.filter(h => h.dia_semana === dayOfWeek && h.ativo) || [];