Preferences: lazy loading on connect, on by default

Off reads the whole app from app.sab when connecting. Read at each connect, so a
change takes effect on the next one.

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

main.py

@@ -2699,6 +2699,18 @@ def open_preferences_dialog():
     )
     chk_trace_dasp.grid(row=5, column=1, sticky="w", pady=(0, 15))
 
+    lbl_lazy = ttk.Label(frame_padded, text="Lazy loading on connect?", anchor="w")
+    lbl_lazy.grid(row=6, column=0, sticky="w", pady=(0, 15), padx=(0, 10))
+
+    # Off: the whole app is read from app.sab when connecting. Takes effect on the next.
+    var_lazy_loading = tk.BooleanVar(value=app_state.LAZY_LOADING)
+    chk_lazy_loading = ttk.Checkbutton(
+        frame_padded,
+        text="Yes",
+        variable=var_lazy_loading
+    )
+    chk_lazy_loading.grid(row=6, column=1, sticky="w", pady=(0, 15))
+
     def apply_preferences():
         try:
             val = int(entry_grid.get().strip())
@@ -2755,6 +2767,7 @@ def open_preferences_dialog():
             app_state.GRID_SIZE = val
             app_state.ADD_TIMESTAMP = var_timestamp.get()
             app_state.TRACE_DASP = var_trace_dasp.get()
+            app_state.LAZY_LOADING = var_lazy_loading.get()
             app_state.SEDONA_HOME = entry_home.get().strip()
 
             app_state.save_preferences()
@@ -2773,7 +2786,7 @@ def open_preferences_dialog():
             messagebox.showerror("Invalid Input", message, parent=dialog)
 
     btn_save_pref = ttk.Button(frame_padded, text="Apply Changes", command=apply_preferences)
-    btn_save_pref.grid(row=6, column=1, sticky="e")
+    btn_save_pref.grid(row=7, column=1, sticky="e")
 
     if not app_state.SEDONA_HOME:
         entry_home.focus_set()