- ContextMenuStrip: select first item on Opened so keyboard-invoked menus
(Shift+F10 / Apps key) raise the UIA focus event immediately instead of
staying silent until the first arrow key.
- Name the SplitContainer/SplitterPanel containers so screen readers announce
orientation instead of a stack of anonymous pane nodes.
- Take the resize splitters out of the Tab cycle (TabStop = false) so focus
moves control-to-control.
- RefreshChannelTree: restore keyboard focus and re-announce the current node
after a Nodes.Clear()/rebuild, so the tree no longer loses focus when
channels/users change.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>