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/MatchingConfigSection.jsx

@@ -1,4 +1,5 @@
 import { useState } from 'react';
+import toast from 'react-hot-toast';
 import { Video, Clock, Save, RefreshCw } from 'lucide-react';
 import { matchingAPI } from '../../services/api';
 
@@ -21,10 +22,11 @@ const MatchingConfigSection = ({ slug, event, onRefresh }) => {
       setSavingDeadline(true);
       const deadline = deadlineInput ? new Date(deadlineInput).toISOString() : null;
       await matchingAPI.setRegistrationDeadline(slug, deadline);
+      toast.success('Deadline saved successfully');
       onRefresh?.();
     } catch (err) {
       console.error('Failed to save deadline:', err);
-      alert('Nie udalo sie zapisac deadline');
+      toast.error('Failed to save deadline');
     } finally {
       setSavingDeadline(false);
     }

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);
     }

frontend/src/pages/EventChatPage.jsx

@@ -1,5 +1,6 @@
 import { useState, useRef, useEffect } from 'react';
 import { useParams, useNavigate, useSearchParams, Link } from 'react-router-dom';
+import toast from 'react-hot-toast';
 import Layout from '../components/layout/Layout';
 import { useAuth } from '../contexts/AuthContext';
 import { Send, UserPlus, Loader2, LogOut, AlertTriangle, QrCode, Edit2, Filter, X, MessageSquare, Users, Video } from 'lucide-react';
@@ -201,7 +202,7 @@ const EventChatPage = () => {
       const result = await matchesAPI.createMatch(userId, slug);
 
       // Show success message
-      alert(`Match request sent successfully! The user will be notified.`);
+      toast.success('Match request sent successfully! The user will be notified.');
 
       // Optional: Navigate to matches page or refresh matches list
       // For now, we just show a success message
@@ -210,13 +211,13 @@ const EventChatPage = () => {
 
       // Show appropriate error message
       if (error.status === 400 && error.message.includes('already exists')) {
-        alert('You already have a match request with this user.');
+        toast.error('You already have a match request with this user.');
       } else if (error.status === 403) {
-        alert('You must be a participant of this event to send match requests.');
+        toast.error('You must be a participant of this event to send match requests.');
       } else if (error.status === 404) {
-        alert('Event not found.');
+        toast.error('Event not found.');
       } else {
-        alert('Failed to send match request. Please try again.');
+        toast.error('Failed to send match request. Please try again.');
       }
     }
   };
@@ -298,7 +299,7 @@ const EventChatPage = () => {
       navigate('/events');
     } catch (error) {
       console.error('Failed to leave event:', error);
-      alert('Failed to leave event. Please try again.');
+      toast.error('Failed to leave event. Please try again.');
     } finally {
       setIsLeaving(false);
       setShowLeaveModal(false);

frontend/src/pages/MatchChatPage.jsx

@@ -1,5 +1,6 @@
 import { useState, useRef, useEffect } from 'react';
 import { useParams, useNavigate, Link } from 'react-router-dom';
+import toast from 'react-hot-toast';
 import Layout from '../components/layout/Layout';
 import { useAuth } from '../contexts/AuthContext';
 import { matchesAPI } from '../services/api';
@@ -73,7 +74,7 @@ const MatchChatPage = () => {
         setMatch(result.data);
       } catch (error) {
         console.error('Failed to load match:', error);
-        alert('Failed to load match. Redirecting to matches page.');
+        toast.error('Failed to load match. Redirecting to matches page.');
         navigate('/matches');
       } finally {
         setLoading(false);
@@ -97,7 +98,7 @@ const MatchChatPage = () => {
     if (file && file.type.startsWith('video/')) {
       setSelectedFile(file);
     } else {
-      alert('Please select a video file');
+      toast.error('Please select a video file');
     }
   };
 
@@ -128,7 +129,7 @@ const MatchChatPage = () => {
       try {
         await waitForConnection;
       } catch (error) {
-        alert('Failed to establish connection: ' + error.message);
+        toast.error('Failed to establish connection: ' + error.message);
         return;
       }
     }

frontend/src/pages/MatchesPage.jsx

@@ -1,5 +1,6 @@
 import { useState, useEffect } from 'react';
 import { useNavigate } from 'react-router-dom';
+import toast from 'react-hot-toast';
 import Layout from '../components/layout/Layout';
 import { useAuth } from '../contexts/AuthContext';
 import { matchesAPI } from '../services/api';
@@ -80,10 +81,10 @@ const MatchesPage = () => {
       await loadMatches();
 
       // Show success message
-      alert('Match accepted! You can now chat with your partner.');
+      toast.success('Match accepted! You can now chat with your partner.');
     } catch (error) {
       console.error('Failed to accept match:', error);
-      alert('Failed to accept match. Please try again.');
+      toast.error('Failed to accept match. Please try again.');
     } finally {
       setProcessingMatchId(null);
     }
@@ -102,7 +103,7 @@ const MatchesPage = () => {
       setMatches(prev => prev.filter(m => m.slug !== matchSlug));
     } catch (error) {
       console.error('Failed to reject match:', error);
-      alert('Failed to reject match. Please try again.');
+      toast.error('Failed to reject match. Please try again.');
     } finally {
       setProcessingMatchId(null);
     }

frontend/src/pages/RatePartnerPage.jsx

@@ -1,5 +1,6 @@
 import { useState, useEffect } from 'react';
 import { useParams, useNavigate } from 'react-router-dom';
+import toast from 'react-hot-toast';
 import Layout from '../components/layout/Layout';
 import { matchesAPI } from '../services/api';
 import { Star, Loader2 } from 'lucide-react';
@@ -26,20 +27,20 @@ const RatePartnerPage = () => {
 
         // Check if this match can be rated
         if (result.data.status !== MATCH_STATUS.ACCEPTED && result.data.status !== MATCH_STATUS.COMPLETED) {
-          alert('This match must be accepted before rating.');
+          toast.error('This match must be accepted before rating.');
           navigate('/matches');
           return;
         }
 
         // Check if user has already rated this match
         if (result.data.hasRated) {
-          alert('You have already rated this match.');
+          toast.info('You have already rated this match.');
           navigate('/matches');
           return;
         }
       } catch (error) {
         console.error('Failed to load match:', error);
-        alert('Failed to load match. Redirecting to matches page.');
+        toast.error('Failed to load match. Redirecting to matches page.');
         navigate('/matches');
       } finally {
         setLoading(false);
@@ -53,7 +54,7 @@ const RatePartnerPage = () => {
   const handleSubmit = async (e) => {
     e.preventDefault();
     if (rating === 0) {
-      alert('Please select a rating (1-5 stars)');
+      toast.warning('Please select a rating (1-5 stars)');
       return;
     }
 
@@ -66,14 +67,14 @@ const RatePartnerPage = () => {
         wouldCollaborateAgain,
       });
 
-      alert('Rating submitted successfully!');
+      toast.success('Rating submitted successfully!');
       navigate('/matches');
     } catch (error) {
       console.error('Failed to submit rating:', error);
       if (error.message?.includes('already rated')) {
-        alert('You have already rated this match.');
+        toast.error('You have already rated this match.');
       } else {
-        alert('Failed to submit rating. Please try again.');
+        toast.error('Failed to submit rating. Please try again.');
       }
     } finally {
       setSubmitting(false);

frontend/src/pages/VerifyEmailPage.jsx

@@ -1,5 +1,6 @@
 import { useState, useEffect } from 'react';
 import { useNavigate, useSearchParams, Link } from 'react-router-dom';
+import toast from 'react-hot-toast';
 import { authAPI } from '../services/api';
 import { useAuth } from '../contexts/AuthContext';
 import { Video, Mail, CheckCircle, XCircle, Loader2, ArrowRight } from 'lucide-react';
@@ -91,7 +92,7 @@ const VerifyEmailPage = () => {
 
     try {
       await authAPI.resendVerification(email);
-      alert('Verification email sent! Please check your inbox.');
+      toast.success('Verification email sent! Please check your inbox.');
     } catch (err) {
       setError(err.data?.error || 'Failed to resend verification email');
     } finally {