Command markers only with the debug setting; removing a marker clears them at once

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

src/render3d.rs

@@ -2908,7 +2908,7 @@ fn draw_marks(g: &Game, t: f32) {
         return;
     }
     for m in &g.marks {
-        if !m.fixed && !g.debug_markers {
+        if !g.debug_markers {
             continue;
         }
         let left = m.until.saturating_sub(g.sim_steps) as f32 * STEP;