Show multi-diff on /import/preview page

[cdrini]

Closes #11405 . Feature. Replace the raw JSON the import preview previously displayed with a diff UI.

Technical

Testing

Screenshot

New records show as JSON:

Stakeholders

[Copilot]

Pull Request Overview

This pull request enhances the import preview functionality by adding diff visualization capabilities and improves responsive design for diff pages. The changes allow users to preview both new records and changes to existing records during the import process, with better mobile responsiveness.

Key Changes:

• Added diff rendering support in import preview with collapsible raw data view
• Improved responsive table layout with no-table-collapse class for diff tables
• Made diff template reusable with optional header parameter and path support
• Refactored CSS for diff pages to use flexbox instead of floats

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
openlibrary/templates/import_preview.html	Added diff visualization for editing existing records and collapsible raw import data view
openlibrary/templates/diff.html	Made template reusable with show_header parameter and improved link handling with path parameter
openlibrary/macros/databarDiff.html	Added path parameter to support diff rendering outside of current page context
openlibrary/plugins/upstream/utils.py	Added create_thing helper function to convert dict data to Thing objects and imported necessary infogami modules
static/css/components/diff.less	Removed float-based layout, added overflow handling, and improved responsive design
static/css/base/common.less	Made table collapse behavior opt-out with no-table-collapse class for diff tables
openlibrary/i18n/messages.pot	Updated translation file with new strings

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