feat(block-editor): add Test Block preview

Preview the current unsaved block in a disposable drawing with independent history. Keep normal Draw tools available, append Close Test Block, and return to the original editor without saving. Guard persistence paths and handle refresh and parent-close lifecycle by stable document identity.

src/ui/ribbon/keytips.rs

@@ -434,6 +434,9 @@ const CODES: &[(&str, &str, &str)] = &[
     ("block_editor", "Open and Save", "BO"),
     ("block_editor", "BEDIT", "BE"),
     ("block_editor", "BSAVE", "BS"),
+    ("block_editor", "BTESTBLOCK", "TB"),
+    ("draw", "Close", "TC"),
+    ("draw", "BCLOSETESTBLOCK", "CT"),
     ("block_editor", "ATTDEF", "AD"),
     ("block_editor", "AUTOCONSTRAIN", "AC"),
     ("block_editor", "CCONSTRAINT", "CI"),
@@ -631,7 +634,7 @@ impl Ribbon {
         };
         let scope = module.id();
         let mut tips = Vec::new();
-        for group in module.ribbon_groups() {
+        for group in self.groups_for(index) {
             for item in &group.tools {
                 match item {
                     RibbonItem::Tool(tool)
@@ -709,11 +712,16 @@ impl Ribbon {
     fn item_tips(&self, index: usize, open: &str) -> Vec<Tip> {
         let mut items = draw_panel::keytip_items(open);
         if items.is_empty() {
-            let groups = self.modules.get(index).map(|m| m.ribbon_groups()).unwrap_or(&[]);
-            for item in groups.iter().flat_map(|group| &group.tools) {
-                if let RibbonItem::Dropdown { id, items: list, .. }
-                | RibbonItem::LabeledDropdown { id, items: list, .. }
-                | RibbonItem::LargeDropdown { id, items: list, .. } = item
+            for item in self.groups_for(index).flat_map(|group| &group.tools) {
+                if let RibbonItem::Dropdown {
+                    id, items: list, ..
+                }
+                | RibbonItem::LabeledDropdown {
+                    id, items: list, ..
+                }
+                | RibbonItem::LargeDropdown {
+                    id, items: list, ..
+                } = item
                 {
                     if *id == open {
                         items = list