feat(frontend): 完成知识对话页面

frontend/src/features/chat/ConversationListPanel.vue

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+<script setup lang="ts">
+import { useChatStore } from '@/stores/chat'
+
+const chatStore = useChatStore()
+</script>
+
+<template>
+  <div class="sidebar-panel">
+    <button class="button-primary new-button" @click="chatStore.createNewConversation">＋ 新对话</button>
+    <div class="sidebar-list conversation-list">
+      <div v-for="conversation in chatStore.sortedConversations" :key="conversation.conversation_id"
+        class="sidebar-list-item conversation" :class="{ active: chatStore.activeConversationId === conversation.conversation_id }"
+        @click="chatStore.setActiveConversation(conversation.conversation_id)">
+        <div><strong>{{ conversation.title }}</strong><p>{{ conversation.message_count }} 条消息</p></div>
+        <button class="delete" title="删除会话" @click.stop="chatStore.deleteConversation(conversation.conversation_id)">×</button>
+      </div>
+    </div>
+  </div>
+</template>
+
+<style scoped>
+.new-button { width: 100%; margin-bottom: var(--space-md); }
+.conversation-list { gap: var(--space-xs); }
+.conversation { display: flex; align-items: center; justify-content: space-between; gap: var(--space-sm); }
+.conversation strong { display: block; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: var(--font-size-sm); }
+.conversation p { color: var(--color-text-tertiary); font-size: var(--font-size-xs); }
+.delete { padding: var(--space-xs); color: var(--color-text-tertiary); }
+</style>