fix(openai): harden GPT-5.6 billing and usage

frontend/src/composables/useModelWhitelist.ts

@@ -8,7 +8,7 @@ const openaiModels = [
   'gpt-5.2', 'gpt-5.2-2025-12-11', 'gpt-5.2-chat-latest',
   'gpt-5.2-pro', 'gpt-5.2-pro-2025-12-11',
   // GPT-5.6 系列
-  'gpt-5.6-sol', 'gpt-5.6-terra', 'gpt-5.6-luna',
+  'gpt-5.6', 'gpt-5.6-sol', 'gpt-5.6-terra', 'gpt-5.6-luna',
   // GPT-5.5 系列
   'gpt-5.5',
   // GPT-5.4 系列
@@ -280,6 +280,7 @@ const openaiPresetMappings = [
   { label: 'o3', from: 'o3', to: 'o3', color: 'bg-emerald-100 text-emerald-700 hover:bg-emerald-200 dark:bg-emerald-900/30 dark:text-emerald-400' },
   { label: 'GPT-5.3 Codex Spark', from: 'gpt-5.3-codex-spark', to: 'gpt-5.3-codex-spark', color: 'bg-teal-100 text-teal-700 hover:bg-teal-200 dark:bg-teal-900/30 dark:text-teal-400' },
   { label: 'GPT-5.2', from: 'gpt-5.2', to: 'gpt-5.2', color: 'bg-red-100 text-red-700 hover:bg-red-200 dark:bg-red-900/30 dark:text-red-400' },
+  { label: 'GPT-5.6', from: 'gpt-5.6', to: 'gpt-5.6', color: 'bg-amber-100 text-amber-700 hover:bg-amber-200 dark:bg-amber-900/30 dark:text-amber-400' },
   { label: 'GPT-5.6 Sol', from: 'gpt-5.6-sol', to: 'gpt-5.6-sol', color: 'bg-orange-100 text-orange-700 hover:bg-orange-200 dark:bg-orange-900/30 dark:text-orange-400' },
   { label: 'GPT-5.6 Terra', from: 'gpt-5.6-terra', to: 'gpt-5.6-terra', color: 'bg-lime-100 text-lime-700 hover:bg-lime-200 dark:bg-lime-900/30 dark:text-lime-400' },
   { label: 'GPT-5.6 Luna', from: 'gpt-5.6-luna', to: 'gpt-5.6-luna', color: 'bg-sky-100 text-sky-700 hover:bg-sky-200 dark:bg-sky-900/30 dark:text-sky-400' },