feat(agent): 支持自建风格与智能体双模式对话系统

- 新增 `source` 字段区分智能体(`agent`)与自建风格(`prompt`)两种对话来源
- 前端统一对话组件，根据来源动态构建请求参数、显示不同样式与文案
- 后端重构 Dify 会话与消息获取逻辑，支持合并查询 Pro 与 Standard 两个 Dify App 的会话历史
- 实现复合游标分页机制，支持跨双数据源的高效分页
- 新增 `clipboard-polyfill` 依赖，统一剪贴板复制功能，提升非 HTTPS 环境兼容性
- 扩展历史记录面板，支持按来源加载对应会话与消息
- 调整侧边抽屉宽度，优化大屏显示体验

frontend/app/web-gold/src/components/agents/ChatDrawerHeader.vue

@@ -1,31 +1,45 @@
 <script setup>
+import { computed } from 'vue'
 import { Icon } from '@iconify/vue'
 import { Button } from '@/components/ui/button'
 
-defineProps({
+const props = defineProps({
   agent: { type: Object, default: null }
 })
 
 const emit = defineEmits(['history'])
 
+const isPromptScene = computed(() => props.agent?.source === 'prompt')
+
 const openHistory = () => emit('history')
 </script>
 
 <template>
   <div class="flex items-center justify-between px-4 py-3 border-b border-border/50 shrink-0 bg-gradient-to-r from-background to-muted/30">
     <div class="flex items-center gap-3">
-      <div class="size-10 rounded-xl bg-gradient-to-br from-primary to-violet-500 flex items-center justify-center overflow-hidden shadow-sm shadow-primary/20">
+      <div
+        class="size-10 rounded-xl flex items-center justify-center overflow-hidden shadow-sm"
+        :class="isPromptScene
+          ? 'bg-gradient-to-br from-amber-400 to-orange-500 shadow-amber-200/30'
+          : 'bg-gradient-to-br from-primary to-violet-500 shadow-primary/20'"
+      >
         <img
           v-if="agent?.avatar"
           :src="agent.avatar"
           :alt="agent.name"
           class="w-full h-full object-cover"
         />
-        <Icon v-else icon="lucide:bot" class="text-white text-xl" />
+        <Icon v-else :icon="isPromptScene ? 'lucide:sparkles' : 'lucide:bot'" class="text-white text-xl" />
       </div>
       <div>
         <div class="font-semibold text-foreground text-sm">{{ agent?.name || 'AI 助手' }}</div>
-        <div class="text-xs text-muted-foreground">{{ agent?.categoryName || '通用' }}</div>
+        <div class="text-xs text-muted-foreground">
+          <span v-if="isPromptScene" class="inline-flex items-center gap-1">
+            <Icon icon="lucide:pencil" class="size-3" />
+            {{ agent?.categoryName || '我的风格' }}
+          </span>
+          <span v-else>{{ agent?.categoryName || '通用' }}</span>
+        </div>
       </div>
     </div>
     <Button