feat(web): use blob download flow in chat info attachment menu

docs/core-checklist-status.md

@@ -22,7 +22,7 @@ Legend:
 13. Reactions - `DONE`
 14. Delivery Status - `DONE` (sent/delivered/read + reconnect reconciliation after backend restarts)
 15. Typing Realtime - `DONE` (web: typing start/stop + recording voice start/stop; `recording_video_*` remains for mobile circle-video clients)
-16. Media & Attachments - `DONE` (upload/preview/download/gallery; sticker/GIF inline media no longer opens photo viewer on click)
+16. Media & Attachments - `DONE` (upload/preview/download/gallery; sticker/GIF inline media no longer opens photo viewer on click; Chat Info and message context menus use blob-download flow with success/error toasts)
 17. Voice Messages - `PARTIAL` (record/send/play/seek + global speed 1x/1.5x/2x; recorder uses improved mime priority for better duration metadata; backend media allowlist includes `audio/mp4`/`audio/x-m4a`; audio store tracks duration via `durationchange/seekable` fallback; websocket send/recorder stop race on fast chat switch is guarded; UX still being polished)
 18. Circle Video Messages - `PARTIAL` (mobile-priority only: backend type/realtime supported; web composer intentionally does not send circles)
 19. Stickers - `PARTIAL` (web sticker picker with preset pack + favorites)

web/src/components/ChatInfoPanel.tsx

@@ -961,9 +961,22 @@ export function ChatInfoPanel({ chatId, open, onClose }: Props) {
           <a className="block rounded px-2 py-1.5 text-sm hover:bg-slate-800" href={attachmentCtx.url} rel="noreferrer" target="_blank">
             Open
           </a>
-          <a className="block rounded px-2 py-1.5 text-sm hover:bg-slate-800" href={attachmentCtx.url} download>
+          <button
+            className="block w-full rounded px-2 py-1.5 text-left text-sm hover:bg-slate-800"
+            onClick={async () => {
+              try {
+                await downloadFileFromUrl(attachmentCtx.url);
+                showToast("File downloaded");
+              } catch {
+                showToast("Download failed");
+              } finally {
+                setAttachmentCtx(null);
+              }
+            }}
+            type="button"
+          >
             Download
-          </a>
+          </button>
           <button
             className="block w-full rounded px-2 py-1.5 text-left text-sm hover:bg-slate-800"
             onClick={async () => {
@@ -1299,3 +1312,20 @@ function shortLink(url: string): string {
     return url;
   }
 }
+
+async function downloadFileFromUrl(url: string): Promise<void> {
+  const response = await fetch(url, { mode: "cors" });
+  if (!response.ok) {
+    throw new Error("Download failed");
+  }
+  const blob = await response.blob();
+  const filename = extractFileName(url);
+  const blobUrl = window.URL.createObjectURL(blob);
+  const link = document.createElement("a");
+  link.href = blobUrl;
+  link.download = filename;
+  document.body.appendChild(link);
+  link.click();
+  link.remove();
+  window.URL.revokeObjectURL(blobUrl);
+}