Card attachment upload only accepts one file at a time (no multi-file support)

[Kazim-Ali-STE]

Description

The card attachment upload UI does not support selecting or dropping multiple files at once — only the first file is ever uploaded, even when multiple files are selected in the file picker or dropped together.

Where

apps/web/src/views/card/components/AttachmentUpload.tsx:

• The file input has no multiple attribute:

  <input
    ref={inputRef}
    type="file"
    id="attachment-upload"
    className="hidden"
    onChange={handleFileSelect}
    disabled={uploading}
  />

• handleFileSelect only reads the first file:

  const handleFileSelect = async (event: React.ChangeEvent<HTMLInputElement>) => {
    const file = event.target.files?.[0];
    if (!file) return;
    ...
    await uploadFile(file);
  };

• handleDrop does the same, and even has a comment acknowledging the limitation:

  const files = Array.from(e.dataTransfer.files);
  if (files.length === 0) return;
  
  // Upload the first file (or could upload all files)
  await uploadFile(files[0] ?? new File([], ""));

Confirmed present in v0.5.5, v0.6.0, and main.

Steps to reproduce

1. Open a card and click the paperclip icon.
2. Select multiple files in the file picker (or drag-and-drop multiple files onto the card).
3. Only the first file gets uploaded; the rest are silently ignored.

Expected behavior

Selecting or dropping multiple files should upload all of them (e.g. sequentially or in parallel), not just the first one.

Suggested fix

• Add multiple to the <input type="file">.
• In both handleFileSelect and handleDrop, iterate over all selected/dropped files and call uploadFile for each (e.g. for (const file of files) { await uploadFile(file); }), rather than only using files[0].