feat: SPLINEDIT — close, open, reverse spline control-point editing

- splinedit.rs: SplineditCommand picks a spline (entity-pick phase) then
  accepts CLOSE/OPEN/REVERSE/EXIT sub-commands via text input
- apply_spline_op() mutates the spline in the document directly, with knot
  vector regeneration via generate_clamped_knots()
- Sentinel XLine trick: ReplaceEntity with a magic __SPLINEDIT_* layer name
  is intercepted in cmd_result.rs before erasing the original entity
- Control-point dragging already works via the existing grip editing system
- ROADMAP.md: SPLINEDIT marked ✅

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

src/app/cmd_result.rs

@@ -170,6 +170,25 @@ impl H7CAD {
                 self.refresh_properties();
             }
             CmdResult::ReplaceEntity(handle, new_entities) => {
+                // Detect SPLINEDIT sentinel: a single XLine with a magic layer name.
+                if new_entities.len() == 1 {
+                    if let acadrust::EntityType::XLine(ref xl) = new_entities[0] {
+                        let op = xl.common.layer.clone();
+                        if op.starts_with("__SPLINEDIT_") {
+                            let label = self.history_label_from_active_cmd(i, "SPLINEDIT");
+                            self.push_undo_snapshot(i, label);
+                            crate::modules::home::modify::splinedit::apply_spline_op(
+                                &mut self.tabs[i].scene.document,
+                                handle,
+                                &op,
+                            );
+                            self.tabs[i].dirty = true;
+                            let prompt = self.tabs[i].active_cmd.as_ref().map(|c| c.prompt());
+                            if let Some(p) = prompt { self.command_line.push_info(&p); }
+                            return Task::none();
+                        }
+                    }
+                }
                 let label = self.history_label_from_active_cmd(i, "TRIM");
                 self.push_undo_snapshot(i, label);
                 self.tabs[i].scene.erase_entities(&[handle]);

src/app/commands.rs

@@ -1435,6 +1435,13 @@ impl H7CAD {
                 self.tabs[i].active_cmd = Some(Box::new(cmd_obj));
             }
 
+            "SPLINEDIT"|"SPE" => {
+                use crate::modules::home::modify::splinedit::SplineditCommand;
+                let cmd_obj = SplineditCommand::new();
+                self.command_line.push_info(&cmd_obj.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(cmd_obj));
+            }
+
             "ALIGN"|"AL" => {
                 use crate::modules::home::modify::align::AlignCommand;
                 let cmd = AlignCommand::new();