feat(web): 添加全局 Toast 通知系统和资产预览导航功能

- 新增 ToastProvider 和 useToast hook，支持全局成功/错误/信息提示
- 资产预览增加左右导航按钮、键盘快捷键(方向键)和计数器显示
- 资产库增加图片/视频类型筛选标签页及计数
- 对话列表增加最近对话展示、搜索优化和删除确认
- 消息增加删除确认对话框
- 优化聊天自动滚动行为，仅在用户未手动滚动时跟随新内容
- 新增删除消息 API 端点
- 优化消息历史清理逻辑，过滤错误消息和孤儿 tool 消息
- 添加自定义滚动条样式
- 优化账户参考图显示逻辑，支持本地文件显示
- 修复对话创建流程，直接导航到新创建的对话

web/server/routes/accounts.ts

@@ -1,5 +1,6 @@
 import { Router } from 'express';
 import fs from 'fs/promises';
+import fss from 'fs';
 import path from 'path';
 import multer from 'multer';
 
@@ -124,6 +125,16 @@ accountsRouter.post('/:id/references/upload', upload.single('file'), async (req,
   res.json({ ok: true, reference: refEntry });
 });
 
+// Serve reference image file
+accountsRouter.get('/:id/references/:filename', (req, res) => {
+  const id = req.params.id as string;
+  const filename = req.params.filename as string;
+  const fullPath = path.join(ACCOUNTS_DIR, id, 'references', filename);
+  if (!fullPath.startsWith(ACCOUNTS_DIR)) return res.status(403).send('Forbidden');
+  if (!fss.existsSync(fullPath)) return res.status(404).send('Not found');
+  res.sendFile(fullPath);
+});
+
 // Reference image delete
 accountsRouter.delete('/:id/references/:index', async (req, res) => {
   const id = req.params.id as string;

web/server/routes/pipeline.ts

@@ -32,8 +32,15 @@ pipelineRouter.get('/conversations/:id/messages', (req, res) => {
 });
 
 pipelineRouter.delete('/conversations/:id', (req, res) => {
+  getDb().prepare('DELETE FROM messages WHERE conversation_id = ?').run(req.params.id);
   getDb().prepare('DELETE FROM conversations WHERE id = ?').run(req.params.id);
-  res.status(204).send();
+  res.json({ ok: true });
+});
+
+// Delete a single message
+pipelineRouter.delete('/messages/:id', (req, res) => {
+  getDb().prepare('DELETE FROM messages WHERE id = ?').run(req.params.id);
+  res.json({ ok: true });
 });
 
 // Update conversation (rename / toggle pin)