feat: download attachments from multiple columns grouped by record

[WhyRoy]

Background

Our organization uses the Teable Community Edition to manage business
records and their related files.

In our workflow, attachments belonging to the same record are often stored
in multiple attachment columns, such as contracts, supporting documents, and
approval materials. When users download these files, they need to select
multiple attachment columns and keep the files belonging to the same record
together.

This change adds an option to download attachments from multiple columns and
organize them by record, so that each record's related files are grouped in
the same folder. This makes the downloaded archive easier to review, share,
and use for offline processing.

Description

Extend bulk attachment downloads to support selecting multiple attachment
columns and organizing their files into folders by record.

This is useful when files belonging to the same record are stored across
different attachment columns and need to be downloaded together.

Changes

• Allow users to select multiple attachment columns in the download dialog.
• Collect attachments from the selected columns for each record.
• Add an option to organize downloaded attachments into folders by record.
• Support choosing a field to name the folders.
• Update the attachment preview totals to reflect the selected columns.

Testing

Manually tested the row-grouped download workflow in a local development
environment. See the screenshot below.

Automated tests were not run in the fork environment.

Screenshot

[CLAassistant]

All committers have signed the CLA.