fix(bot): IsComplete must not flag null MaxPlayers as missing (no-limit)

After 3.9.6 fixed long-polling, the bot finally reaches the final
'✅ Создать' step. Users pressing '♾ Без лимита' on the Capacity step
get a valid payload where Single.MaxPlayers = null (the legitimate
no-limit choice from GameCreationWizard.ApplyCapacityChoice 'no_limit'),
but CreateSessionHandler.IsComplete then reports 'лимит мест' as
missing, blocking session creation.

This regression existed since 3.9.3 (when 'no_limit' was added) but
stayed invisible because 3.9.4 and 3.9.5 never reached SubmitDraft
(libgssapi-krb5 missing → long-polling hung). Once 3.9.6 restored
polling, the bug surfaced immediately.

Fix: drop the null-MaxPlayers check from IsComplete for Single type.
Null is a valid 'no limit' state and must pass through to BuildCommands
→ shared handler, which already accepts null MaxPlayers correctly.

Closes #131.

Bump version 3.9.6 -> 3.9.7

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <Version>3.9.6</Version>
+    <Version>3.9.7</Version>
     <TargetFramework>net10.0</TargetFramework>
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>