* Fix WiFi network selection in TUI prompt
TableSelectionScreen returns the selected network in Result._item,
but the check on line 136 only tested Result._data (always None
for single-select). This caused every selection to fall through
to the "No wifi networks found" error path.
Fixes#4564
* Fix empty wifi scan crash and simplify network selection
Move wifi scanning out of the TableSelectionScreen callback to avoid
MenuItemGroup([]) ValueError when no networks are found. The empty
result is now handled before the selection screen, and the Selection
branch is simplified to a direct get_value() call.