* test(ui): split test_ui_regressions into domain modules

* test(ui): restore rationale comments lost in the split

Restore the code_contains docstring, which docs/development.md relies on to
explain why qmlformat spacing does not break membership assertions, and the
coverage pointers that record where account and session response semantics
are tested instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test(ui): fix malformed compound code_contains assertions

* test(ui): split compound UI regression assertions

---------

Co-authored-by: Simone <185146821+Lucenx9@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
Co-authored-by: Grok Bot <grok-bot@users.noreply.github.com>