This pull request updates the Mail app’s user interface foundation by introducing OWL-based components and related template support. It should make messaging screens such as Discuss, chat windows, composers, attachments, and autocomplete more maintainable and ready for future improvements, though some upload-related tests were temporarily disabled due to hard-to-reproduce runbot race conditions.

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:




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