Ensure mission exists before inserting mission launch entity

src/MissionControl.Server/Endpoints/Missions/MissionLaunches/CreateMissionLaunch.cs

@@ -1,5 +1,6 @@
 using FastEndpoints;
 using FluentValidation;
+using Microsoft.EntityFrameworkCore;
 using MissionControl.Data;
 using MissionControl.Domain.Entities;
 
@@ -15,6 +16,13 @@ public class CreateMissionLaunch(MissionControlContext dbContext)
 
     public override async Task HandleAsync(CreateMissionLaunchRequest req, CancellationToken ct)
     {
+        var missionExists = await dbContext.Missions.AnyAsync(mission => mission.Id == req.MissionId, ct);
+        if (!missionExists)
+        {
+            await Send.NotFoundAsync(ct);
+            return;
+        }
+
         var missionLaunch = new MissionLaunch
         {
             ScheduledFor = req.ScheduledFor,