review fixes: complete success path, pool capacity navigation, time parser tests

- DiscordWizardSubmitter.SubmitAsync: confirm success, delete draft, clear context.
- GameCreationWizard: pool free-text duration now advances to Capacity.
- PreviousStep(Capacity) returns PoolSystemDuration for pools.
- Remove unused optional IPlatformMessenger/NpgsqlDataSource from submitter.
- Add DiscordTimeParserTests preserving ParseTimeInput coverage.

src/GmRelay.Shared/Features/Sessions/CreateSession/Wizard/GameCreationWizard.cs

@@ -256,7 +256,7 @@ public sealed class GameCreationWizard
 
             case WizardStepNames.PoolSystemDuration when payload.DurationMinutes is null:
                 return TryParseHours(input, out var pdur)
-                    ? (WizardStepNames.Format, SetDurationMinutes(payload, pdur), payload)
+                    ? (WizardStepNames.Capacity, SetDurationMinutes(payload, pdur), payload)
                     : (null, "Неверная длительность (1..12 ч)", payload);
 
             case WizardStepNames.PoolSlotDateTime:
@@ -421,7 +421,7 @@ public sealed class GameCreationWizard
         WizardStepNames.System => WizardStepNames.Cover,
         WizardStepNames.Duration => WizardStepNames.System,
         WizardStepNames.DateTime => WizardStepNames.Duration,
-        WizardStepNames.Capacity => WizardStepNames.DateTime,
+        WizardStepNames.Capacity => p.Type == WizardCreationType.Pool ? WizardStepNames.PoolSystemDuration : WizardStepNames.DateTime,
         WizardStepNames.Format => WizardStepNames.Capacity,
         WizardStepNames.Location => WizardStepNames.Format,
         WizardStepNames.Visibility => WizardStepNames.Location,