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/widgets/glass_card.dart

@@ -0,0 +1,53 @@
+import 'dart:ui';
+import 'package:flutter/material.dart';
+
+class GlassCard extends StatelessWidget {
+  const GlassCard({
+    super.key,
+    required this.child,
+    this.padding = const EdgeInsets.all(16),
+    this.margin,
+    this.borderRadius = 16,
+    this.blur = 10,
+    this.backgroundColor,
+    this.borderColor,
+  });
+
+  final Widget child;
+  final EdgeInsetsGeometry padding;
+  final EdgeInsetsGeometry? margin;
+  final double borderRadius;
+  final double blur;
+  final Color? backgroundColor;
+  final Color? borderColor;
+
+  @override
+  Widget build(BuildContext context) {
+    final effectiveBackground =
+        backgroundColor ?? const Color(0xFF1E293B).withOpacity(0.6);
+    final effectiveBorder =
+        borderColor ?? Colors.white.withOpacity(0.08);
+
+    Widget card = ClipRRect(
+      borderRadius: BorderRadius.circular(borderRadius),
+      child: BackdropFilter(
+        filter: ImageFilter.blur(sigmaX: blur, sigmaY: blur),
+        child: Container(
+          padding: padding,
+          decoration: BoxDecoration(
+            color: effectiveBackground,
+            borderRadius: BorderRadius.circular(borderRadius),
+            border: Border.all(color: effectiveBorder, width: 1),
+          ),
+          child: child,
+        ),
+      ),
+    );
+
+    if (margin != null) {
+      return Container(margin: margin, child: card);
+    }
+
+    return card;
+  }
+}