feat: add complete review/rating system for events

New feature: Users can view, submit, and interact with event reviews.

Components added:
- ReviewModel, ReviewStatsModel, ReviewListResponse (models)
- ReviewService with getReviews, submitReview, markHelpful, flagReview
- StarRatingInput (interactive 5-star picker with labels)
- StarDisplay (read-only fractional star display)
- ReviewSummary (average rating + distribution bars)
- ReviewForm (star picker + comment field + submit/update)
- ReviewCard (avatar, timestamp, expandable comment, helpful/flag)
- ReviewSection (main container with pagination and state mgmt)

Integration:
- Added to LearnMoreScreen (both mobile and desktop layouts)
- Review API endpoints point to app.eventifyplus.com Node.js backend
- EventModel updated with averageRating/reviewCount fields

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

lib/core/api/api_endpoints.dart

@@ -28,6 +28,13 @@ class ApiEndpoints {
   // static const String userSuccessBookings = "$baseUrl/events/event/user-success-bookings/";
   // static const String userCancelledBookings = "$baseUrl/events/event/user-cancelled-bookings/";
 
+  // Reviews (served by Node.js backend via app.eventifyplus.com)
+  static const String _reviewBase    = "https://app.eventifyplus.com/api/reviews";
+  static const String reviewSubmit   = "$_reviewBase/submit";
+  static const String reviewList     = "$_reviewBase/list";
+  static const String reviewHelpful  = "$_reviewBase/helpful";
+  static const String reviewFlag     = "$_reviewBase/flag";
+
   // Gamification / Contributor Module (TechDocs v2)
   static const String gamificationProfile = "$baseUrl/v1/user/gamification-profile/";
   static const String leaderboard         = "$baseUrl/v1/leaderboard/";