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

pubspec.yaml

@@ -19,6 +19,7 @@ dependencies:
   google_maps_flutter: ^2.5.0
   url_launcher: ^6.2.1
   share_plus: ^7.2.1
+  path_provider: ^2.1.0
   provider: ^6.1.2
   video_player: ^2.8.1
   cached_network_image: ^3.3.1
@@ -39,6 +40,7 @@ flutter:
     - assets/images/
     - assets/icon/hand_stop.svg
     - assets/login-bg.mp4
+    - assets/data/kerala_pincodes.json
   fonts:
     - family: Gilroy
       fonts: