Fix tree expand in live mode: use focused item and run IO in background

_on_tree_open used tree.selection() which may differ from the opened
node; switched to tree.focus(). Network calls in _live_tree_expand now
run in a daemon thread so the UI stays responsive during lazy loading.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app_state.py

@@ -8,7 +8,7 @@ so later rebinding would only ever be seen by the module that did it.
 import configparser
 import os
 
-VERSION = "0.0.0.078"
+VERSION = "0.0.0.079"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True