Add screen reader support for chat list

[rezabakhshilaktasaraei]

Summary

Exposes painted dialog rows as virtual accessibility children, making the chat list fully navigable by screen readers.

Changes (dialogs_inner_widget.cpp/h, dialogs_widget.cpp)

• Overrides accessibilityChildCount(), accessibilityChildName(), accessibilityChildRect(), accessibilityChildState(), accessibilityChildRole(), and column sub-item methods.
• Each dialog row becomes a ListItem with a descriptive name built from:
  • Chat type prefix: Channel / Group / Bot / Topic / Folder
  • Badges: Verified, Scam, Fake
  • Status: Pinned, Online, Unread count, Mentions, Stories
  • Last message: Sender + preview text, delivery status (Sending/Sent/Failed/Received), draft indicator
  • Special rows: Saved Messages sublists, Sponsored, Auto-delete, Subscribed
• 23 multi-column sub-items for structured screen reader navigation (type, name, warning, activity, muted, pinned, draft, unread, sender, message, delivery, reactions, time, etc.)
• Fires accessibilityChildFocused() on keyboard navigation.
• Arrow key / PageUp / PageDown / Space navigation is now guarded by hasFocus() to prevent unintended list movement when focus is elsewhere.

Dependencies

• Requires lib_ui#278 for Accessible::Item infrastructure.

New lang keys

~55 new lng_sr_chat_* keys + lng_sr_from_me, lng_sr_message_seen, lng_sr_message_not_seen.

Test plan

• Navigate chat list with arrow keys — screen reader announces each chat with type, name, badges, and last message
• Verify topics, folders, saved message sublists are announced correctly
• Verify hit-testing: clicking a row with screen reader cursor selects the correct chat
• Verify arrow keys do not move chat list selection when focus is on another widget (e.g., search field)