fix: correct 3d axis tick orientation and avoid duplicate 2d labels (#1351)

## Summary
- flip the 3D X-axis tick marks and labels so they render beneath the
axis in device space
- skip drawing the legacy 2D tick labels when 3D plots are active while
still rendering the axis title/x/y labels

## Testing
- make verify-artifacts

------
https://chatgpt.com/codex/tasks/task_e_68cd9f2942248324b0b3feb6167d67cd

Author: krystophny

src/backends/raster/fortplot_raster.f90

@@ -20,6 +20,7 @@ module fortplot_raster
     use fortplot_raster_core, only: raster_image_t, create_raster_image, destroy_raster_image
     use fortplot_raster_axes, only: raster_draw_axes_and_labels, raster_render_ylabel, &
                                         raster_draw_axes_lines_and_ticks, raster_draw_axis_labels_only
+    use fortplot_raster_labels, only: raster_draw_axis_labels
     use fortplot_raster_rendering, only: raster_fill_heatmap, raster_fill_quad, fill_triangle, &
                                         raster_render_legend_specialized, raster_calculate_legend_dimensions, &
                                         raster_set_legend_border_width, raster_calculate_legend_position, &
@@ -456,7 +457,8 @@ subroutine raster_draw_axes_and_labels_context(this, xscale, yscale, symlog_thre
         character(len=:), allocatable, intent(in), optional :: title, xlabel, ylabel
         real(wp), intent(in), optional :: z_min, z_max
         logical, intent(in) :: has_3d_plots
-        
+        character(len=:), allocatable :: title_str, xlabel_str, ylabel_str
+
         ! Set color to black for axes and text
         call this%color(0.0_wp, 0.0_wp, 0.0_wp)
 
@@ -465,12 +467,24 @@ subroutine raster_draw_axes_and_labels_context(this, xscale, yscale, symlog_thre
             call draw_3d_axes(this, x_min, x_max, y_min, y_max, &
                               merge(z_min, 0.0_wp, present(z_min)), &
                               merge(z_max, 1.0_wp, present(z_max)))
-            ! Draw title/xlabel/ylabel using existing raster helpers for labels only
+            ! Draw title/xlabel/ylabel without re-drawing 2D tick labels
             if (present(title) .or. present(xlabel) .or. present(ylabel)) then
-                call raster_draw_axis_labels_only(this%raster, this%width, this%height, this%plot_area, &
-                                                 xscale, yscale, symlog_threshold, &
-                                                 x_min, x_max, y_min, y_max, &
-                                                 title, xlabel, ylabel)
+                title_str = ""
+                xlabel_str = ""
+                ylabel_str = ""
+
+                if (present(title)) then
+                    if (allocated(title)) title_str = title
+                end if
+                if (present(xlabel)) then
+                    if (allocated(xlabel)) xlabel_str = xlabel
+                end if
+                if (present(ylabel)) then
+                    if (allocated(ylabel)) ylabel_str = ylabel
+                end if
+
+                call raster_draw_axis_labels(this%raster, this%width, this%height, this%plot_area, &
+                                             title_str, xlabel_str, ylabel_str)
             end if
         else
             ! Delegate to standard 2D axes module

src/plotting/fortplot_3d_axes.f90

@@ -226,11 +226,14 @@ subroutine draw_3d_axis_ticks_and_labels(ctx, corners_2d, x_min, x_max, y_min, y
         real(wp) :: x_range, y_range
         real(wp) :: tick_len_y, tick_len_x
         real(wp) :: pad_x, pad_y
+        real(wp) :: tick_y_end, label_y_pos
+        real(wp) :: y_span
         integer :: decimals_x, decimals_y, decimals_z
 
         ! Use fractions of the current data ranges for tick lengths and padding
-        x_range = max(1.0e-12_wp, x_max - x_min)
-        y_range = max(1.0e-12_wp, y_max - y_min)
+        x_range = max(1.0e-12_wp, abs(x_max - x_min))
+        y_span = y_max - y_min
+        y_range = max(1.0e-12_wp, abs(y_span))
         tick_len_y = 0.02_wp * y_range   ! vertical tick length (in data units)
         tick_len_x = 0.02_wp * x_range   ! horizontal tick length (in data units)
         pad_x = 0.02_wp * x_range        ! horizontal text padding (data units)
@@ -252,13 +255,22 @@ subroutine draw_3d_axis_ticks_and_labels(ctx, corners_2d, x_min, x_max, y_min, y
             ! Interpolate position along edge
             x_pos = corners_2d(1,1) + (corners_2d(1,2) - corners_2d(1,1)) * real(i-1, wp) / real(n_ticks-1, wp)
             y_pos = corners_2d(2,1) + (corners_2d(2,2) - corners_2d(2,1)) * real(i-1, wp) / real(n_ticks-1, wp)
-            
-            ! Draw tick mark pointing down (in data units)
-            call ctx%line(x_pos, y_pos, x_pos, y_pos + tick_len_y)
-            
+
+            ! Determine downward direction in device space based on Y span sign
+            if (y_span >= 0.0_wp) then
+                tick_y_end = y_pos - tick_len_y
+                label_y_pos = tick_y_end - pad_y
+            else
+                tick_y_end = y_pos + tick_len_y
+                label_y_pos = tick_y_end + pad_y
+            end if
+
+            ! Draw tick mark pointing down in device space
+            call ctx%line(x_pos, y_pos, x_pos, tick_y_end)
+
             ! Draw label using consistent decimal places across the axis
             label = format_tick_value_consistent(value, decimals_x)
-            call render_text_to_ctx(ctx, x_pos - 0.5_wp*pad_x, y_pos + tick_len_y + pad_y, trim(adjustl(label)))
+            call render_text_to_ctx(ctx, x_pos - 0.5_wp*pad_x, label_y_pos, trim(adjustl(label)))
         end do
 
         ! Y-axis ticks and labels (edge from corner 1 to corner 4)