v7 beta feedback: please consider custom dropdowns instead of native <select>/<datalist>

I love the more modern redesign. One change that feels like a step back in daily use is the switch to native browser dropdowns throughout the UI. • Inconsistent look: native menus render differently in each browser and OS (e.g., a dark OS-styled popup in Edge on macOS) and don't match the rest of the admin UI. • Harder to use: v6's multi-select stayed open while choosing several items. The new list picker's native <datalist> popup closes after every selection, so choosing several lists means reopening the dropdown for each one, which is noticeably slower than the v6 multi-select with chips. It also seems to be behind #3301, where selected lists are removed when clicking outside the field. • Less predictable: behavior differs between browsers, which makes the UI harder to learn. • Feels unfamiliar to existing users: our team includes non-technical staff who use listmonk regularly. During user testing of the beta, several weren't sure h…