feat: Phase 3 — 26 medium-priority gaps implemented

P3-A/K  Profile: Eventify ID glassmorphic badge (tap-to-copy), DiceBear
        Notionists avatar via TierAvatarRing, district picker (14 pills)
        with 183-day cooldown lock, multipart photo upload to server
P3-B    Home: Top Events converted to PageView scroll-snap
        (viewportFraction 0.9 + PageScrollPhysics)
P3-C    Event detail: contributor widget (tier ring + name + navigation),
        related events horizontal row; added getEventsByCategory() to
        EventsService; added contributorId/Name/Tier fields to EventModel
P3-D    Kerala pincodes: 463-entry JSON (all 14 districts), registered as
        asset, async-loaded in SearchScreen replacing hardcoded 32 cities
P3-E    Checkout: promo code field + Apply/Remove button in Step 2,
        discountAmount subtracted from total, applyPromo()/resetPromo()
        methods in CheckoutProvider
P3-F/G  Gamification: reward cycle countdown + EP→RP progress bar (blue→
        amber) in contribute + profile screens; TierAvatarRing in podium
        and all leaderboard rows; GlassCard current-user stats card at
        top of leaderboard tab
P3-H    New ContributorProfileScreen: tier ring, stats, submission grid
        with status chips; getDashboardForUser() in GamificationService;
        wired from leaderboard row taps
P3-I    Achievements: 11 default badges (up from 6), 6 new icon map
        entries; progress % labels already confirmed present
P3-J    Reviews: CustomPainter circular arc rating ring (amber, 84px)
        replaces large rating number in ReviewSummary
P3-L    Share rank card: RepaintBoundary → PNG capture → Share.shareXFiles;
        share button wired in profile header and leaderboard tab
P3-M    SafeArea audit: home bottom nav, contribute/achievements scroll
        padding, profile CustomScrollView top inset

New files: tier_avatar_ring.dart, glass_card.dart,
  eventify_bottom_sheet.dart, contributor_profile_screen.dart,
  share_rank_card.dart, assets/data/kerala_pincodes.json
New dep:   path_provider ^2.1.0

lib/features/booking/providers/checkout_provider.dart

@@ -1,6 +1,10 @@
 // lib/features/booking/providers/checkout_provider.dart
 
+import 'dart:convert';
 import 'package:flutter/foundation.dart';
+import 'package:http/http.dart' as http;
+import 'package:shared_preferences/shared_preferences.dart';
+import '../../../core/api/api_endpoints.dart';
 import '../../../core/utils/error_utils.dart';
 import '../models/booking_models.dart';
 import '../services/booking_service.dart';
@@ -24,8 +28,11 @@ class CheckoutProvider extends ChangeNotifier {
   // Shipping
   ShippingDetails? shippingDetails;
 
-  // Coupon
+  // Coupon / promo
   String? couponCode;
+  double discountAmount = 0.0;
+  String? promoMessage;
+  bool promoApplied = false;
 
   // Status
   bool loading = false;
@@ -40,6 +47,9 @@ class CheckoutProvider extends ChangeNotifier {
     cart = [];
     shippingDetails = null;
     couponCode = null;
+    discountAmount = 0.0;
+    promoMessage = null;
+    promoApplied = false;
     paymentId = null;
     error = null;
     loading = true;
@@ -65,7 +75,7 @@ class CheckoutProvider extends ChangeNotifier {
   }
 
   double get subtotal => cart.fold(0, (sum, item) => sum + item.subtotal);
-  double get total => subtotal; // expand with discount/tax later
+  double get total => subtotal - discountAmount;
 
   bool get hasItems => cart.isNotEmpty;
 
@@ -95,6 +105,62 @@ class CheckoutProvider extends ChangeNotifier {
     notifyListeners();
   }
 
+  /// Apply a promo code against the backend.
+  Future<bool> applyPromo(String code) async {
+    if (code.trim().isEmpty) return false;
+    loading = true;
+    error = null;
+    notifyListeners();
+    try {
+      final prefs = await SharedPreferences.getInstance();
+      final token = prefs.getString('access_token') ?? '';
+      final response = await http.post(
+        Uri.parse('${ApiEndpoints.baseUrl}/bookings/apply-promo/'),
+        headers: {
+          'Content-Type': 'application/json',
+          'Authorization': 'Bearer $token',
+        },
+        body: jsonEncode({'code': code.trim(), 'event_id': eventId}),
+      );
+      if (response.statusCode == 200) {
+        final data = jsonDecode(response.body);
+        if (data['valid'] == true) {
+          discountAmount = (data['discount_amount'] as num?)?.toDouble() ?? 0.0;
+          couponCode = code.trim();
+          promoMessage = data['message'] as String? ?? 'Promo applied!';
+          promoApplied = true;
+          notifyListeners();
+          return true;
+        } else {
+          promoMessage = data['message'] as String? ?? 'Invalid promo code';
+          promoApplied = false;
+          discountAmount = 0.0;
+          couponCode = null;
+          notifyListeners();
+          return false;
+        }
+      } else {
+        promoMessage = 'Could not apply promo code';
+        return false;
+      }
+    } catch (e) {
+      promoMessage = 'Could not apply promo code';
+      return false;
+    } finally {
+      loading = false;
+      notifyListeners();
+    }
+  }
+
+  /// Remove applied promo code.
+  void resetPromo() {
+    discountAmount = 0.0;
+    couponCode = null;
+    promoMessage = null;
+    promoApplied = false;
+    notifyListeners();
+  }
+
   /// Process checkout on backend.
   Future<Map<String, dynamic>> processCheckout() async {
     loading = true;
@@ -139,6 +205,9 @@ class CheckoutProvider extends ChangeNotifier {
     cart = [];
     shippingDetails = null;
     couponCode = null;
+    discountAmount = 0.0;
+    promoMessage = null;
+    promoApplied = false;
     paymentId = null;
     error = null;
     loading = false;