chore(viewer): update grid overlay button tooltips

Align hover hint text with draw_crosshair rename.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Evgeni Raikhel

common/stream-model.cpp

@@ -601,7 +601,7 @@ namespace rs2
                 show_grid = false;
             }
             if (ImGui::IsItemHovered())
-                RsImGui::CustomTooltip("Hide grid overlay");
+                RsImGui::CustomTooltip("Hide crosshair/grid overlay");
             ImGui::PopStyleColor(2);
         }
         else
@@ -611,7 +611,7 @@ namespace rs2
                 show_grid = true;
             }
             if (ImGui::IsItemHovered())
-                RsImGui::CustomTooltip("Show grid overlay");
+                RsImGui::CustomTooltip("Show crosshair/grid overlay");
         }
         ImGui::SameLine();