feat: add kimi-k3 preset to model configs

kimi-k3: Moonshot flagship (2.8T MoE, 1M context), single model ID
on api.moonshot.cn/v1, pricing $3/$15 per 1M tokens (display hint).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/ModelConfigs.vue

@@ -376,6 +376,7 @@ function createModelGroups(): ProviderGroup[] {
     {
       provider: 'moonshot', label: '月之暗面 Kimi', defaultBaseUrl: 'https://api.moonshot.cn/v1',
       models: [
+        { name: 'kimi-k3', desc: 'K3 旗舰 2.8T/1M上下文', price: '$3/15', checked: false },
         { name: 'kimi-k2-0905-preview', desc: 'K2 增强版', price: '¥4/16', checked: false },
         { name: 'kimi-k2-0711-preview', desc: 'K2 旗舰', price: '¥4/16', checked: false },
         { name: 'kimi-k2-turbo-preview', desc: 'K2 高速版', price: '¥8/32', checked: false },