feat: ATTREQ — attribute prompting during INSERT

When inserting a block that contains AttributeDefinition entities,
the INSERT command now enters an attribute-filling phase: each attdef
is prompted tag-by-tag (showing its prompt text and default value).
Pressing Enter accepts the default. The completed AttributeEntity list
is embedded in the Insert before committing.

Blocks without attdefs continue to insert immediately as before.

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

src/app/cmd_result.rs

@@ -256,6 +256,50 @@ impl H7CAD {
                     self.command_line.push_info(&p);
                 }
             }
+            CmdResult::AttreqNeeded { block_name } => {
+                // Collect AttributeDefinitions owned by this block record.
+                let attdefs: Vec<(String, String, String)> = {
+                    let doc = &self.tabs[i].scene.document;
+                    if let Some(br) = doc.block_records.get(&block_name) {
+                        br.entity_handles.iter().filter_map(|&h| {
+                            if let Some(acadrust::EntityType::AttributeDefinition(ad)) =
+                                doc.get_entity(h)
+                            {
+                                Some((ad.tag.clone(), ad.prompt.clone(), ad.default_value.clone()))
+                            } else {
+                                None
+                            }
+                        }).collect()
+                    } else {
+                        vec![]
+                    }
+                };
+
+                if attdefs.is_empty() {
+                    // No attribute definitions — commit the INSERT directly.
+                    let entity = self.tabs[i].active_cmd.as_mut()
+                        .and_then(|c| c.attreq_take_insert());
+                    if let Some(entity) = entity {
+                        let label = self.history_label_from_active_cmd(i, "INSERT");
+                        self.push_undo_snapshot(i, label);
+                        self.commit_entity(entity);
+                        self.tabs[i].dirty = true;
+                        self.tabs[i].scene.clear_preview_wire();
+                        self.tabs[i].active_cmd = None;
+                        self.tabs[i].snap_result = None;
+                        self.restore_pre_cmd_tangent();
+                    }
+                } else {
+                    // Inject attdefs so the command enters attr-filling mode.
+                    if let Some(cmd) = &mut self.tabs[i].active_cmd {
+                        cmd.attreq_set_attdefs(attdefs);
+                    }
+                    let prompt = self.tabs[i].active_cmd.as_ref().map(|c| c.prompt());
+                    if let Some(p) = prompt {
+                        self.command_line.push_info(&p);
+                    }
+                }
+            }
             CmdResult::Cancel => {
                 self.tabs[i].scene.clear_preview_wire();
                 self.tabs[i].active_cmd = None;