Support screen reader focus and activate on chat list rows

[rezabakhshilaktasaraei]

The chat list rows are painted/virtual (no real QWidget), so a screen reader couldn't move focus to a row or activate one. With the action interface from desktop-app/lib_ui#303, those requests now reach InnerWidget:

• Move focus → accessibilityChildSetFocus, Activate → accessibilityChildActivate. Both hop to the main thread (UIA invokes actions on a background thread) and are dispatched by stable row identity (peer / entry / result pointer), so a reordered or replaced row is never acted on by mistake.
• An explicit accessibility SetFocus is honored directly — it is not gated on the screen-reader-mode detector, which can still be false during startup or for valid clients that aren't on its allowlist.
• Selection and activation share selectChildByIndex(), which first clears secondary mouse hit-test state (hashtag delete, "more posts", chat-type filter, topic-jump, right button) so an Invoke can't trigger one of those instead of opening the row.
• Default-state accessibility (count / name / state / rect / columns + selection) now goes through one mapping shared with painting and keyboard navigation — collapsed rows first, then the shown list with _skipTopDialog applied — and the collapsed Archive row is exposed.

Depends on desktop-app/lib_ui#303; CI won't compile until that is merged and the submodule updated.