补充 VP 模块注册 + 前端 API 封装

- app.module.ts: 注册 VirtualPaymentModule
- config.ts + api.ts: 添加虚拟支付 API 端点
- useGravityPurchase.ts: VP 购买逻辑
- interview.vue / user.vue: 适配 VP 调用
- admin.controller.ts: 管理端虚拟支付相关调整
- payment.controller.spec.ts: 测试适配

backend/src/modules/payment/payment.controller.spec.ts

@@ -36,12 +36,12 @@ describe('PaymentController', () => {
     }
     mockPricingService = {
       getConfig: jest.fn().mockResolvedValue({
-        interview: { pricePerSession: 500, creditsPerPurchase: 1 },
-        resumeOptimize: { freeLimit: 3, pricePerOptimize: 300, creditsPerPurchase: 1 },
+        interview: { pricePerSession: 600, creditsPerPurchase: 1 },
+        resumeOptimize: { freeLimit: 3, pricePerOptimize: 400, creditsPerPurchase: 1 },
         resumeDownload: { pricePerDownload: 200, creditsPerPurchase: 1 },
         plans: {
-          growth: { price: 1990, durationDays: 30, gravityPerMonth: 250, credits: { interview: 999, resumeOptimize: 20, resumeDownload: 10 }, features: [] },
-          sprint: { price: 4990, durationDays: 30, gravityPerMonth: 600, credits: { interview: 999, resumeOptimize: 50, resumeDownload: 30 }, features: [] },
+          growth: { price: 1990, durationDays: 30, gravityPerMonth: 80, credits: { interview: 999, resumeOptimize: 20, resumeDownload: 10 }, features: [] },
+          sprint: { price: 4990, durationDays: 30, gravityPerMonth: 200, credits: { interview: 999, resumeOptimize: 50, resumeDownload: 30 }, features: [] },
         },
       }),
     }
@@ -158,7 +158,7 @@ describe('PaymentController', () => {
       expect(result.plan).toBe('growth')
       expect(mockUser.save).toHaveBeenCalled()
       expect(mockUser.plan).toBe('growth')
-      expect(mockUser.gravity).toBe(250)
+      expect(mockUser.gravity).toBe(80)
       expect(mockUser.freeOptimizeUsed).toBe(3)
     })