fix: MiniMax 已到期，切换 primary tier 到 DeepSeek V4 Pro

- model-router: primary 层 preferred 从 minimax-m2.7 改为 deepseek-v4-pro
- cost-calculator: 移除 minimax 零成本豁免
- billing: MiniMax 标注已到期

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/admin-billing/admin-billing.service.ts

@@ -34,6 +34,6 @@ export class AdminBillingService {
     } catch { return { name: '硅基流动', model: 'Embedding/Rerank', balance: '—', currency: 'CNY', status: 'unknown', consoleUrl: 'https://cloud.siliconflow.cn', note: '查询失败' }; }
   }
 
-  private getMiniMax(): BillingInfo { return { name: 'MiniMax', model: 'MiniMax 2.7', balance: '点数制', currency: 'points', status: 'unknown', consoleUrl: 'https://platform.minimaxi.com', note: '需登录控制台查看' }; }
+  private getMiniMax(): BillingInfo { return { name: 'MiniMax', model: 'MiniMax 2.7', balance: '已到期', currency: '—', status: 'unknown', consoleUrl: 'https://platform.minimaxi.com', note: '已到期，已切换至 DeepSeek V4' }; }
   private getBaiduOcr(): BillingInfo { return { name: '百度 OCR', model: '通用文字识别', balance: '次数制', currency: 'calls', status: 'unknown', consoleUrl: 'https://console.bce.baidu.com', note: '需登录控制台查看' }; }
 }

src/modules/ai/model-router.ts

@@ -23,7 +23,7 @@ const DEFAULT_ROUTES: Record<string, TierConfig> = {
   },
   primary: {
     tier: 'primary',
-    preferred: { provider: 'minimax', model: 'minimax-m2.7' },
+    preferred: { provider: 'deepseek', model: 'deepseek-v4-pro' },
     fallback: { provider: 'deepseek', model: 'deepseek-v4-pro' },
     maxRetries: 3,
   },

src/modules/ai/usage/ai-cost-calculator.service.ts

@@ -13,7 +13,7 @@ export class AiCostCalculatorService {
   };
 
   calculate(provider: string, model: string, inputTokens: number, outputTokens: number): number {
-    if (provider === 'mock' || provider === 'minimax') return 0;
+    if (provider === 'mock') return 0;
 
     const tier = this.pricing[model];
     if (!tier) return 0;