fix(admin): 赠送流量配置项补全中英文案并修正语义描述

- 补提交 giftTraffic i18n key（此前仅表单落库，中文界面显示英文兜底）
- 修正描述：0=时长模式（按试用时长配置），>0=流量模式不限时用完为止
  （原文案「0=不限流量」与后端实际语义相反，会误导运营配置）

apps/admin/src/sections/system/user-security/register-form.tsx

@@ -41,6 +41,7 @@ const registerSchema = z.object({
   trial_subscribe: z.number().optional(),
   trial_time: z.number().optional(),
   trial_time_unit: z.string().optional(),
+  gift_traffic: z.number().optional(),
   enable_trial_email_whitelist: z.boolean().optional(),
   trial_email_domain_whitelist: z.string().optional(),
   enable_ip_register_limit: z.boolean().optional(),
@@ -75,6 +76,7 @@ export default function RegisterConfig() {
       trial_subscribe: undefined,
       trial_time: 0,
       trial_time_unit: "day",
+      gift_traffic: 0,
       enable_trial_email_whitelist: false,
       trial_email_domain_whitelist: "",
       enable_ip_register_limit: false,
@@ -449,6 +451,40 @@ export default function RegisterConfig() {
                     )}
                   />
 
+                  <FormField
+                    control={form.control}
+                    name="gift_traffic"
+                    render={({ field }) => (
+                      <FormItem>
+                        <FormLabel>
+                          {t("register.giftTraffic", "Gift Traffic")}
+                        </FormLabel>
+                        <FormControl>
+                          <EnhancedInput
+                            min={0}
+                            onValueBlur={(value) =>
+                              field.onChange(Number(value))
+                            }
+                            placeholder={t(
+                              "register.inputPlaceholder",
+                              "Please enter"
+                            )}
+                            suffix="GB"
+                            type="number"
+                            value={field.value}
+                          />
+                        </FormControl>
+                        <FormDescription>
+                          {t(
+                            "register.giftTrafficDescription",
+                            "Gift traffic for new users (GB). 0 = duration mode (uses the trial duration above); >0 = quota mode: N GB with no time limit, trial duration is ignored"
+                          )}
+                        </FormDescription>
+                        <FormMessage />
+                      </FormItem>
+                    )}
+                  />
+
                   <FormField
                     control={form.control}
                     name="enable_trial_email_whitelist"