Add a Properties view for the app root

The root tree row now names the app component, "app (<host:port>)" or
"app (<file>)", and offers Properties from its context menu and on
double-click. The live DOM's <app> element now carries its type and slot
values, and the refresh-by-id lookup finds it, so the view shows real
sys::App values.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sax_file.py

@@ -64,12 +64,13 @@ def refresh_treeview_from_dom(xml_root):
         return
 
     if app_state.live_mode:
-        file_name = f"{app_state.device_host}:{app_state.device_port}"
+        source = f"{app_state.device_host}:{app_state.device_port}"
     else:
-        file_name = os.path.basename(app_state.current_file_path)
+        source = os.path.basename(app_state.current_file_path)
+    # The row is the <app> component itself; where it came from goes in brackets.
     # Inserted plain. refresh_dirty_display puts the unsaved tag on or off, and runs
     # after every rebuild, so a fresh row picks up the right state there.
-    root_node = tree.insert("", "end", text=file_name, open=True)
+    root_node = tree.insert("", "end", text=f"app ({source})", open=True)
 
     app_element = xml_root.find("app")
     if app_element is not None: