feat(backend): add problem/need submission module with workflow and events

Add submission CRUD with pagination and role scoping, challenge/location binding, automatic keyword extraction, a validated status workflow, and domain events for matchmaking and notifications. Create a problem record together with each submission.

backend/Infrastructure/DependencyInjection.cs

@@ -3,6 +3,7 @@ using Microsoft.Extensions.DependencyInjection;
 using SurrealDb.Net;
 using TarninaHub.Application.Abstractions;
 using TarninaHub.Infrastructure.Auth;
+using TarninaHub.Infrastructure.Events;
 using TarninaHub.Infrastructure.Persistence;
 using TarninaHub.Infrastructure.Settings;
 
@@ -52,6 +53,8 @@ public static class DependencyInjection
         services.AddSingleton<IUserService, UserService>();
         services.AddSingleton<IConsentService, ConsentService>();
         services.AddSingleton<IAuditLogService, AuditLogService>();
+        services.AddSingleton<ISubmissionEventPublisher, LoggingSubmissionEventPublisher>();
+        services.AddSingleton<ISubmissionService, SubmissionService>();
 
         return services;
     }