refactor(frontend): replace alert() with modern toast notifications

Replaced all alert() calls with react-hot-toast notifications for better
user experience. Toast notifications are non-blocking, auto-dismiss, and
provide visual feedback with icons based on message type.

Changes:
- EventChatPage: Match request success/error toasts
- MatchChatPage: Video file selection and WebRTC connection error toasts
- MatchesPage: Match accept/reject action toasts
- RatePartnerPage: Rating submission and validation toasts
- VerifyEmailPage: Email verification sent toast
- ScheduleConfigSection: Schedule save success/error toasts
- MatchingConfigSection: Deadline save success/error toasts

All toast notifications use appropriate types (success, error, warning, info)
for better visual distinction and user feedback.

frontend/src/components/events/ScheduleConfigSection.jsx

@@ -1,4 +1,5 @@
 import { useState, useEffect } from 'react';
+import toast from 'react-hot-toast';
 import { Layers, Plus, Trash2, Save, RefreshCw } from 'lucide-react';
 import { matchingAPI, divisionsAPI } from '../../services/api';
 
@@ -72,10 +73,11 @@ const ScheduleConfigSection = ({ slug, event, onRefresh }) => {
         ? { slots: scheduleSlots.filter(s => s.divisionIds.length > 0) }
         : null;
       await matchingAPI.setScheduleConfig(slug, scheduleConfig);
+      toast.success('Schedule saved successfully');
       onRefresh?.();
     } catch (err) {
       console.error('Failed to save schedule:', err);
-      alert('Nie udalo sie zapisac harmonogramu');
+      toast.error('Failed to save schedule');
     } finally {
       setSavingSchedule(false);
     }