Wiresheet: grey margin strip, saved-state tint on and off the sheet

- The top/left margin no box may enter is grey and ungridded, so the white
  sheet starts where boxes can actually be placed.
- Saving/unsaved state no longer resets the canvas to white: the sheet goes
  white/pink and the area around it grey/greyish pink.

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

wiresheet.py

@@ -123,7 +123,6 @@ FIT_PADDING = 20
 # as a grey wash rather than a grid, so the grid is left off instead.
 MIN_GRID_STEP = 3
 SHEET_MARGIN_GRIDS = 3  # grid squares of grey kept past anything that overflows the sheet
-OFF_SHEET_COLOUR = "#f3f3f3"  # canvas outside the area a box's origin can be stored in
 
 
 def snap_up(value, grid_size):
@@ -240,16 +239,18 @@ def measure_box(comp, fonts, linked_slot_index):
 
 
 def draw_grid():
-    """Paints the sheet white and grids it; the canvas around it stays OFF_SHEET_COLOUR.
+    """Paints the sheet and grids it; the canvas around it is the off-sheet tint.
 
     Drawn at the sheet's zoom, so a box still lands on a line at every scale.
     """
     canvas = app_state.canvas
     canvas.delete("grid")
 
-    x1, y1 = 0, 0
+    # The sheet starts past the margin strip no box may enter, which stays grey too.
+    x1 = y1 = layout_margin(app_state.meta_scale) * app_state.zoom
     x2, y2 = (coord * app_state.zoom for coord in sheet_extent())
-    canvas.create_rectangle(x1, y1, x2, y2, fill="white", outline="#c8c8c8", tags="grid")
+    canvas.create_rectangle(x1, y1, x2, y2, outline="#c8c8c8", tags=("grid", "sheet_bg"))
+    app_state.paint_sheet_tint()   # white or pink by saved state, grey or pink around it
 
     step = app_state.GRID_SIZE * app_state.zoom
     if step >= MIN_GRID_STEP: