feat(grid): the coloured grid axis lines can be turned off (#1815)

Drafting Settings > Snap and Grid gains "Display grid axis lines",
kept with the other grid settings; the grid itself stays as it is.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/update/file.rs

@@ -925,6 +925,7 @@ impl OpenCADStudio {
             grid_major_every: self.grid_major_every,
             grid_adaptive: self.grid_adaptive,
             grid_beyond_limits: self.grid_beyond_limits,
+            grid_axes: self.grid_axes,
             block_mru: self.block_mru.clone(),
             block_freq: self.block_freq.clone(),
             block_recent: self.block_palette.recent.clone(),
@@ -1110,6 +1111,7 @@ impl OpenCADStudio {
         self.grid_major_every = crate::app::settings::sanitize_grid_major(s.grid_major_every);
         self.grid_adaptive = s.grid_adaptive;
         self.grid_beyond_limits = s.grid_beyond_limits;
+        self.grid_axes = s.grid_axes;
         // Block usage: clone but cap to sane sizes (MRU 20, freq map 200)
         self.block_mru = s.block_mru.iter().take(20).cloned().collect();
         self.block_freq = s

src/app/update/mod.rs

@@ -6401,6 +6401,12 @@ impl OpenCADStudio {
                 }
                 Task::none()
             }
+            Message::DraftingSettingsToggleGridAxes => {
+                if let Some(state) = &mut self.drafting_settings_state {
+                    state.grid_axes = !state.grid_axes;
+                }
+                Task::none()
+            }
             Message::DraftingSettingsToggleEqualSnap => {
                 if let Some(state) = &mut self.drafting_settings_state {
                     state.snap_equal = !state.snap_equal;