feat: Phase 2 — 11 high-priority gaps implemented across home, auth, gamification, profile, and event detail

Phase 2 gaps completed:
- HOME-001: Hero slider pause-on-touch (GestureDetector wraps PageView)
- HOME-003: Calendar bottom sheet with TableCalendar (replaces custom dialog)
- AUTH-004: District dropdown on signup (14 Kerala districts)
- EVT-003: Mobile sticky "Book Now" bar + desktop CTA wired to CheckoutScreen
- ACH-001: Real achievements from dashboard API with fallback defaults
- GAM-002: 3-card EP row (Lifetime EP / Liquid EP / Reward Points)
- GAM-005: Horizontal tier roadmap Bronze→Silver→Gold→Platinum→Diamond
- CTR-001: Submission status chips (PENDING/APPROVED/REJECTED)
- CTR-002: +EP badge on approved submissions
- PROF-003: Gamification cards on profile screen with Consumer<GamificationProvider>
- UX-001: Shimmer skeleton loaders (shimmer ^3.0.0) replacing CircularProgressIndicator

Already complete (verified, no changes needed):
- HOME-002: Category shelves already built in _buildTypeSection()
- LDR-002: Podium visualization already built (_buildPodium / _buildDesktopPodium)
- BOOK-004: UPI handled natively by Razorpay SDK

Deferred: LOC-001/002 (needs Django haversine endpoint)
Skipped: AUTH-002 (OTP needs SMS provider decision)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/widgets/skeleton_loader.dart

@@ -0,0 +1,134 @@
+import 'package:flutter/material.dart';
+import 'package:shimmer/shimmer.dart';
+
+/// Generic shimmer rectangle with configurable dimensions and border radius.
+class SkeletonBox extends StatelessWidget {
+  final double width;
+  final double height;
+  final double borderRadius;
+
+  const SkeletonBox({
+    Key? key,
+    this.width = double.infinity,
+    required this.height,
+    this.borderRadius = 8,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final isDark = Theme.of(context).brightness == Brightness.dark;
+    return Shimmer.fromColors(
+      baseColor: isDark ? const Color(0xFF2D2D2D) : Colors.grey[300]!,
+      highlightColor: isDark ? const Color(0xFF3D3D3D) : Colors.grey[100]!,
+      child: Container(
+        width: width,
+        height: height,
+        decoration: BoxDecoration(
+          color: Colors.white,
+          borderRadius: BorderRadius.circular(borderRadius),
+        ),
+      ),
+    );
+  }
+}
+
+/// Shimmer placeholder for a compact event card (used in horizontal lists).
+class EventCardSkeleton extends StatelessWidget {
+  const EventCardSkeleton({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      width: 200,
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: const [
+          SkeletonBox(height: 140, borderRadius: 12),
+          SizedBox(height: 8),
+          SkeletonBox(height: 14, width: 160),
+          SizedBox(height: 6),
+          SkeletonBox(height: 12, width: 100),
+        ],
+      ),
+    );
+  }
+}
+
+/// Shimmer placeholder for a full-width event list row.
+class EventListSkeleton extends StatelessWidget {
+  const EventListSkeleton({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.symmetric(vertical: 6, horizontal: 16),
+      child: Row(
+        children: const [
+          SkeletonBox(width: 64, height: 64, borderRadius: 10),
+          SizedBox(width: 12),
+          Expanded(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                SkeletonBox(height: 14),
+                SizedBox(height: 8),
+                SkeletonBox(height: 12, width: 140),
+              ],
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+/// Shimmer placeholder for hero carousel area.
+class HeroCarouselSkeleton extends StatelessWidget {
+  const HeroCarouselSkeleton({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const Padding(
+      padding: EdgeInsets.symmetric(horizontal: 16),
+      child: SkeletonBox(height: 320, borderRadius: 24),
+    );
+  }
+}
+
+/// Shimmer grid for achievements tab.
+class AchievementGridSkeleton extends StatelessWidget {
+  const AchievementGridSkeleton({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return GridView.count(
+      crossAxisCount: 2,
+      shrinkWrap: true,
+      physics: const NeverScrollableScrollPhysics(),
+      mainAxisSpacing: 12,
+      crossAxisSpacing: 12,
+      padding: const EdgeInsets.all(16),
+      children: List.generate(4, (_) => const SkeletonBox(height: 160, borderRadius: 16)),
+    );
+  }
+}
+
+/// Shimmer placeholder for profile stat cards row.
+class ProfileStatsSkeleton extends StatelessWidget {
+  const ProfileStatsSkeleton({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
+      child: Row(
+        children: List.generate(3, (_) => const Expanded(
+          child: Padding(
+            padding: EdgeInsets.symmetric(horizontal: 4),
+            child: SkeletonBox(height: 80, borderRadius: 12),
+          ),
+        )),
+      ),
+    );
+  }
+}