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

compose.yaml

@@ -49,7 +49,7 @@ services:
         crond -f
 
   bot:
-    image: git.codeanddice.ru/toutsu/gmrelay-bot:3.9.6
+    image: git.codeanddice.ru/toutsu/gmrelay-bot:3.9.7
     restart: always
     depends_on:
       db:
@@ -67,7 +67,7 @@ services:
       retries: 3
 
   discord:
-    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:3.9.6
+    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:3.9.7
     restart: always
     depends_on:
       db:
@@ -86,7 +86,7 @@ services:
       retries: 3
 
   web:
-    image: git.codeanddice.ru/toutsu/gmrelay-web:3.9.6
+    image: git.codeanddice.ru/toutsu/gmrelay-web:3.9.7
     restart: always
     depends_on:
       db: