Use /launches instead of /launch since there are now multiple

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

@@ -11,7 +11,7 @@ public class CreateMissionLaunch(MissionControlContext dbContext)
 {
     public override void Configure()
     {
-        Post("/missions/{MissionId}/launch");
+        Post("/missions/{MissionId}/launches");
     }
 
     public override async Task HandleAsync(CreateMissionLaunchRequest req, CancellationToken ct)

src/mission-control-client/src/api/missionLaunches.ts

@@ -27,7 +27,7 @@ export async function createMissionLaunch(
   request: CreateMissionLaunchRequest,
 ): Promise<MissionLaunch> {
   const response = await apiClient.post<MissionLaunch>(
-    `/missions/${request.missionId}/launch`,
+    `/missions/${request.missionId}/launches`,
     request,
   );
   return response.data;