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/features/events/models/event_models.dart

@@ -68,6 +68,10 @@ class EventModel {
   // Structured important info list [{title, value}, ...]
   final List<Map<String, String>> importantInfo;
 
+  // Review stats (populated when backend includes them)
+  final double? averageRating;
+  final int? reviewCount;
+
   EventModel({
     required this.id,
     required this.name,
@@ -91,6 +95,8 @@ class EventModel {
     this.longitude,
     this.locationName,
     this.importantInfo = const [],
+    this.averageRating,
+    this.reviewCount,
   });
 
   /// Safely parse a double from backend (may arrive as String or num)
@@ -148,6 +154,8 @@ class EventModel {
       longitude: _parseDouble(j['longitude']),
       locationName: j['location_name'] as String?,
       importantInfo: _parseImportantInfo(j['important_info']),
+      averageRating: (j['average_rating'] as num?)?.toDouble(),
+      reviewCount: (j['review_count'] as num?)?.toInt(),
     );
   }
 }