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/features/auth/services/auth_service.dart

@@ -78,15 +78,20 @@ class AuthService {
     required String email,
     required String phoneNumber,
     required String password,
+    String? district,
   }) async {
     try {
+      final body = <String, dynamic>{
+        "email": email,
+        "phone_number": phoneNumber,
+        "password": password,
+      };
+      if (district != null && district.isNotEmpty) {
+        body["district"] = district;
+      }
       final res = await _api.post(
         ApiEndpoints.register,
-        body: {
-          "email": email,
-          "phone_number": phoneNumber,
-          "password": password,
-        },
+        body: body,
         requiresAuth: false,
       );