feat(contribute): upload event images to OneDrive before submission

- ApiClient.uploadFile() — multipart POST to /v1/upload/file (60s timeout)
- ApiEndpoints.uploadFile — points to Node.js upload endpoint
- GamificationService.submitContribution() now uploads each picked image
  to OneDrive via the server upload pipeline, then passes the returned
  { fileId, url, ... } objects as `media` in the submission body
  (replaces broken behaviour of sending local device paths as strings)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/core/api/api_endpoints.dart

@@ -14,6 +14,7 @@ class ApiEndpoints {
   static const String login = "$baseUrl/user/login/";
   static const String logout = "$baseUrl/user/logout/";
   static const String status = "$baseUrl/user/status/";
+  static const String updateProfile = "$baseUrl/user/update-profile/";
 
   // Events
   static const String eventTypes = "$baseUrl/events/type-list/";             // list of event types
@@ -22,6 +23,8 @@ class ApiEndpoints {
   static const String eventImages = "$baseUrl/events/event-images/";        // event-images
   static const String eventsByCategory = "$baseUrl/events/events-by-category/";
   static const String eventsByMonth = "$baseUrl/events/events-by-month-year/";
+  static const String featuredEvents = "$baseUrl/events/featured-events/";
+  static const String topEvents = "$baseUrl/events/top-events/";
 
   // Bookings
   // static const String bookEvent = "$baseUrl/events/book-event/";
@@ -38,6 +41,9 @@ class ApiEndpoints {
   // Node.js gamification server (same host as reviews)
   static const String _nodeBase = "https://app.eventifyplus.com/api";
 
+  // File upload (Node.js — routes to OneDrive or GDrive via STORAGE_BACKEND env)
+  static const String uploadFile = "$_nodeBase/v1/upload/file";
+
   // Gamification / Contributor Module
   static const String gamificationDashboard = "$_nodeBase/v1/gamification/dashboard";
   static const String leaderboard           = "$_nodeBase/v1/gamification/leaderboard";