feat(plan): 添加储蓄GS多阶段产品2年缴费期选项

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

@@ -52,3 +52,9 @@ describe('critical illness mpc special age options', () => {
     expect(PLAN_TEMPLATES['critical-illness-mbc2'].config.special_age_options).toBeUndefined()
   })
 })
+
+describe('savings gs multistage payment periods', () => {
+  it('should include 2-year payment period option', () => {
+    expect(PLAN_TEMPLATES['savings-gs-multistage'].config.payment_periods).toContain('2 年')
+  })
+})

@@ -408,6 +408,7 @@ export const PLAN_TEMPLATES = {
       currency: 'USD',
       payment_periods: [
         '整付',
+        '2 年',
         '3 年',
         '5 年',
         '10 年',