Issue #3611743: UX review — filters, copy, exports, CTA, pagination

Jérôme Tchaniarequested to merge
issue/ai_metering-3611743:1.0.x-3611743-ux-review into 1.0.x

Closes #3611743

Replaces the AI Usage Log filters with Choices.js, trims the by-role "(preview)" copy, consolidates CSV/JSON export into one dropbutton across all three pages, adds a per-editor -> by-role CTA, and paginates both breakdown tables at 10/page with LIMIT/OFFSET in SQL.

AI assistance

Yes.

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