fix(tui): avoid NoMatches exception when SelectionList is missing on key events.

[hrshtmk]

Summary

Fixes an unhandled NoMatches crash when key events (such as Backspace) occur on a SelectListScreen while SelectionList is not mounted or active.

Problem

In archinstall/tui/components.py, SelectListScreen.on_key() previously called self.query_one(SelectionList) directly. If a keystroke arrives during rapid navigation or screen dismissal, an unhandled NoMatches exception is thrown, causing archinstall to crash:

NoMatches: No nodes match 'SelectionList' on SelectListScreen()

• Note : This crash happened when I was installing arch on my own physical hardware. Triggering the timing window inside a QEMU VM was difficult to replicate on demand due to input latencies, but the trace proves the unhandled exception path.

Fix

Updated SelectListScreen.on_key() to query SelectionList using .query().first():

selection_list = self.query(SelectionList).first()
if not selection_list or not selection_list.has_focus or event.key != 'enter':
    return