Redesign files pages to support new UI

[nlhkabu]

As part of the work to implement attestations best practices, I am proposing to redesign the files UI to:

1. Surface attestation metadata during file browsing
2. Surface security warnings in the files UI
3. Take advantage of the full width of the page (now that the main menu will be displayed as horizontal tabs)

Files (scenario: with file added late)

Interactive prototype (desktop only): https://claude.ai/public/artifacts/7ba6bcc6-5b86-46c9-8065-73c0158dd25a

This design builds on the terrific work completed by @cofiem in #18741, adding provenance status and flagging any files added late.

As per #19951, I suggest that we display this warning for any file added to a release 24 hours or more after the first file is uploaded.

File detail (scenario: with provenance)

Interactive prototype (desktop only): https://claude.ai/public/artifacts/1e58e013-0204-442e-9434-1ed6ae3cc88b

[nlhkabu]

Note - need to include #20045 in this UI