feat: implement real-time notification toast system

Implemented comprehensive notification toast system integrating Socket.IO
with react-toastify for real-time user notifications.

Features:
- NotificationProvider component for automatic Socket.IO event handling
- Custom Bootstrap-themed toast styles with mobile responsiveness
- Four toast types: success, error, info, warning
- Auto-dismiss after 5 seconds with manual dismiss option
- Duplicate prevention using toast IDs
- Mobile-optimized full-width toasts
- Dark mode support
- 16 passing tests with full coverage

Toast notifications for:
- Connection status (connect/disconnect/reconnect)
- Event updates (new, updated, deleted, participants)
- Task updates (new, completed, updated, deleted)
- Street adoptions/unadoptions
- Achievement unlocks and badge awards
- Social updates (new posts, comments)
- Generic notifications with type-based styling

Usage:
import { notify } from '../context/NotificationProvider';
notify.success('Operation completed!');
notify.error('Something went wrong!');

Configuration:
- Position: top-right (configurable)
- Auto-close: 5 seconds (configurable)
- Max toasts: 5 concurrent
- Mobile responsive: full-width on ≤480px screens

Documentation:
- NOTIFICATION_SYSTEM.md: Complete usage guide
- NOTIFICATION_IMPLEMENTATION.md: Implementation summary
- frontend/src/examples/notificationExamples.js: Code examples

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

NOTIFICATION_IMPLEMENTATION.md

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+# Notification Toast System - Implementation Summary
+
+## Overview
+Implemented a comprehensive real-time notification toast system for the Adopt-a-Street frontend application. The system integrates Socket.IO events with react-toastify to provide user-friendly notifications for all real-time events.
+
+## Files Created
+
+### 1. NotificationProvider Component
+**Path:** `frontend/src/context/NotificationProvider.js`
+- Integrates with SocketContext and AuthContext
+- Automatically listens to Socket.IO events and displays toasts
+- Provides `notify` utility for manual toast triggering
+- Handles connection status, events, tasks, streets, achievements, and social updates
+
+### 2. Custom Toast Styles
+**Path:** `frontend/src/styles/toastStyles.css`
+- Custom CSS matching Bootstrap theme colors
+- Mobile-responsive design (full-width on screens ≤480px)
+- Support for success, error, info, and warning toast types
+- Smooth animations and hover effects
+- Dark mode support
+
+### 3. Usage Examples
+**Path:** `frontend/src/examples/notificationExamples.js`
+- Comprehensive examples of using the notification system
+- Demonstrates notify utility, toast API, promises, and async patterns
+- Example component showing real-world usage
+
+### 4. Documentation
+**Path:** `NOTIFICATION_SYSTEM.md`
+- Complete documentation of the notification system
+- Usage instructions and examples
+- Socket.IO event mappings
+- Configuration options
+- Troubleshooting guide
+
+### 5. Tests
+**Path:** `frontend/src/__tests__/context/NotificationProvider.test.js`
+- 16 passing tests covering all functionality
+- Tests for event subscriptions, toast triggering, cleanup
+- Tests for notify utility functions
+
+## Files Modified
+
+### 1. App.js
+**Changes:**
+- Added import for `NotificationProvider` and custom styles
+- Wrapped Router with NotificationProvider
+- Enhanced ToastContainer configuration:
+  - Increased autoClose to 5000ms
+  - Set newestOnTop to true
+  - Added theme="light"
+  - Added limit={5} to prevent toast spam
+
+### 2. setupTests.js
+**Changes:**
+- Added global axios mock to prevent test import errors
+
+## How to Trigger Toasts from Components
+
+### Method 1: Using notify utility (Recommended)
+```javascript
+import { notify } from "../context/NotificationProvider";
+
+notify.success("Operation completed!");
+notify.error("Something went wrong!");
+notify.info("Here's some info");
+notify.warning("Be careful!");
+```
+
+### Method 2: Using toast directly
+```javascript
+import { toast } from "react-toastify";
+
+toast.success("Success message");
+toast.error("Error message", { autoClose: 3000 });
+```
+
+### Method 3: For async operations
+```javascript
+const toastId = toast.loading("Processing...");
+// ... do work ...
+toast.update(toastId, {
+  render: "Completed!",
+  type: "success",
+  isLoading: false,
+});
+```
+
+## Socket.IO Events That Trigger Notifications
+
+### Connection Events
+- `connect` → Success: "Connected to real-time updates"
+- `disconnect` → Error/Warning: Connection lost messages
+- `reconnect` → Success: "Reconnected to server"
+- `reconnect_error` → Error: "Failed to reconnect"
+
+### Event Updates (`eventUpdate`)
+- `new_event` → Info: "New event: [event title]"
+- `event_updated` → Info: "Event details have been updated"
+- `event_deleted` → Warning: "An event has been cancelled"
+
+### Task Updates (`taskUpdate`)
+- `new_task` → Info: "New task available: [task description]"
+- `task_completed` → Success: "Task completed by another user"
+- `task_updated` → Info: "A task has been updated"
+- `task_deleted` → Warning: "A task has been removed"
+
+### Street Updates (`streetUpdate`)
+- `street_adopted` → Info: "[Street] was adopted by [User]"
+- `street_unadopted` → Info: "[Street] is now available"
+
+### Achievements
+- `achievementUnlocked` → Success: Custom achievement toast with badge details
+- `badgeUnlocked` → Success: Custom badge toast with details
+
+### Social Updates
+- `newPost` → Info: "[User] created a new post"
+- `newComment` → Info: "[User] commented on a post"
+
+### Generic Notifications
+- `notification` → Type-based: Fallback for custom notifications
+
+## Configuration Options
+
+### ToastContainer Options (in App.js)
+- **position**: `top-right` (also available: top-left, top-center, bottom-*)
+- **autoClose**: `5000` (5 seconds, set to `false` for persistent)
+- **hideProgressBar**: `false` (show progress bar)
+- **newestOnTop**: `true` (stack newest on top)
+- **limit**: `5` (max 5 toasts at once)
+- **theme**: `light` (also available: dark, colored)
+- **pauseOnHover**: `true` (pause auto-dismiss on hover)
+- **draggable**: `true` (can drag to dismiss)
+
+### Individual Toast Options
+```javascript
+notify.success("Message", {
+  autoClose: 3000,
+  position: "bottom-right",
+  toastId: "unique-id", // Prevent duplicates
+  pauseOnHover: false,
+  closeOnClick: true,
+});
+```
+
+## Mobile Responsiveness
+- **Desktop**: Positioned in top-right corner with 320px width
+- **Mobile (≤480px)**: Full-width toasts at the top of screen
+- Touch-friendly dismissal
+- Optimized animations for mobile
+
+## Testing
+All tests passing (16/16):
+```bash
+cd frontend && npm test -- --testPathPattern="NotificationProvider" --watchAll=false
+```
+
+## Build Status
+✅ Production build successful
+✅ No errors or breaking changes
+✅ All existing tests still passing
+
+## Next Steps (Optional Enhancements)
+1. Add notification sound effects (configurable)
+2. Add notification history/center
+3. Add user preferences for notification types
+4. Add desktop notifications API integration
+5. Add notification grouping for similar events
+6. Add undo/action buttons in toasts
+
+## Backend Integration Notes
+To trigger notifications from backend, emit Socket.IO events:
+
+```javascript
+const io = req.app.get("io");
+
+// Notify all users
+io.emit("notification", {
+  type: "info",
+  message: "System maintenance in 5 minutes",
+});
+
+// Notify specific user
+io.to(userSocketId).emit("achievementUnlocked", {
+  badge: { name: "Badge Name", description: "Description" },
+});
+
+// Notify room
+io.to(`event_${eventId}`).emit("eventUpdate", {
+  type: "participants_updated",
+  eventId,
+  participants: [...],
+});
+```
+
+## Resources
+- Full documentation: `NOTIFICATION_SYSTEM.md`
+- Usage examples: `frontend/src/examples/notificationExamples.js`
+- Tests: `frontend/src/__tests__/context/NotificationProvider.test.js`
+- react-toastify docs: https://fkhadra.github.io/react-toastify/