fix: move agent attachment download api (#15146)

### What problem does this PR solve?

move agent attachment download api to the correct route and update
frontend callers

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### Notes

- Move the attachment download endpoint from document routes to agent
routes.
- Update frontend download callers to use the agent attachment endpoint.
- Reuse the shared file response header helper instead of duplicating it
in `agent_api.py`.

web/src/components/document-download-button/index.tsx

@@ -1,6 +1,6 @@
 import { Button } from '@/components/ui/button';
 import { IDocumentDownloadInfo } from '@/interfaces/database/chat';
-import { downloadFile } from '@/services/file-manager-service';
+import { downloadAgentFile } from '@/services/file-manager-service';
 import { downloadFileFromBlob } from '@/utils/file-util';
 import { Download, FileText } from 'lucide-react';
 import { useCallback } from 'react';
@@ -20,7 +20,7 @@ export function DocumentDownloadButton({
     try {
       const ext =
         downloadInfo.filename.split('.').pop()?.toLowerCase() || 'bin';
-      const response = await downloadFile({
+      const response = await downloadAgentFile({
         docId: downloadInfo.doc_id,
         ext,
       });

web/src/components/next-message-item/group-button.tsx

@@ -8,7 +8,7 @@ import {
 import { useSetModalState } from '@/hooks/common-hooks';
 import { IRemoveMessageById } from '@/hooks/logic-hooks';
 import { AgentChatContext } from '@/pages/agent/context';
-import { downloadFile } from '@/services/file-manager-service';
+import { downloadAgentFile } from '@/services/file-manager-service';
 import { downloadFileFromBlob } from '@/utils/file-util';
 import {
   DeleteOutlined,
@@ -125,7 +125,7 @@ export const AssistantGroupButton = ({
             value="g"
             onClick={async () => {
               try {
-                const response = await downloadFile({
+                const response = await downloadAgentFile({
                   docId: attachment.doc_id,
                   ext: attachment.format,
                 });