feat(card): attach files directly when creating a card

[HeinrichNebula]

What

The new-card modal only supports title/description/labels/members/due date. Attaching a file requires creating the card first, reopening it, and uploading there. This PR lets users queue files in the create form itself:

• Paperclip button (hidden multi-file input) plus drag & drop onto the form
• Queued files render as removable chips below the option row
• On submit, the card is created first, then the files are uploaded sequentially to the existing /api/upload/attachment endpoint, followed by a board invalidation
• If the card mutation fails, the queue is restored so a retry keeps the files
• If some uploads fail, the card is kept and a popup reports how many attachments failed (no rollback)
• "Create another" clears the queue

Also removes duplicate comments/checklists/attachments keys in the optimistic card payload in the same file (TS1117, a hard error under tsc --noEmit).

Notes

• Files are kept in component state, not in the persisted modal form state (File objects do not survive serialization)
• No new endpoints or schema changes; reuses the upload path and its 50MB limit
• i18n via the existing lingui t macros

Testing

• Create card with 2 files: both appear as attachments on the created card
• Create card without files: behavior unchanged
• Upload failure (oversized file): card exists, popup reports the failed count
• "Create another": queue resets between cards