feat(steward): 前端支持 off_topic 与引导话术

- assistantSessionScope.js：新增 ASSISTANT_SCOPE_ACTION_FILL_COMPOSER 常量
- assistantSuggestedActionPrefill.js：识别 fill_composer 与 payload.fill_text
- stewardPlanModel.js：normalizeStewardPlan 透传 suggestedPrompts；
  buildStewardPlanMessageText / buildStewardSuggestedActions
  新增 off_topic 分支，按钮填充输入框不提交
- useStewardPlanFlow.js：isPendingStewardActionMessage 排除 off_topic
- steward-plan-off-topic.test.mjs：覆盖 normalize/文案/按钮/兼容路径

web/src/views/scripts/useStewardPlanFlow.js

@@ -2,6 +2,7 @@ import {
   buildStewardPlanMessageText,
   buildStewardPlanRequest,
   buildStewardSuggestedActions,
+  isOffTopicStewardPlan,
   normalizeStewardPlan
 } from './stewardPlanModel.js'
 import { SESSION_TYPE_STEWARD } from './travelReimbursementConversationModel.js'
@@ -384,7 +385,14 @@ export function useStewardPlanFlow({
 
   function isPendingStewardActionMessage(message) {
     if (message?.stewardPlan) {
-      return message.stewardPlan.streamStatus !== 'streaming'
+      if (message.stewardPlan.streamStatus === 'streaming') {
+        return false
+      }
+      // off_topic 是引导用户重新编辑输入，不参与"确定/确认"快捷回复链路。
+      if (isOffTopicStewardPlan(message.stewardPlan)) {
+        return false
+      }
+      return true
     }
     return (
       String(message?.assistantName || '').trim() === '小财管家'