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/modules/block_editor/mod.rs

@@ -63,6 +63,11 @@ impl CadModule for BlockEditorModule {
                             "Close Block Editor",
                             include_bytes!("../../../assets/icons/mt_cancel.svg"),
                         ),
+                        command(
+                            "BTESTBLOCK",
+                            "Test Block",
+                            include_bytes!("../../../assets/icons/edit_block.svg"),
+                        ),
                     ],
                 },
                 RibbonGroup {

src/modules/draw/mod.rs

@@ -15,7 +15,7 @@ mod report;
 pub mod select;
 pub mod units;
 
-use crate::modules::{CadModule, RibbonGroup, RibbonItem};
+use crate::modules::{CadModule, IconKind, ModuleEvent, RibbonGroup, RibbonItem, ToolDef};
 
 pub struct DrawModule;
 
@@ -249,6 +249,15 @@ impl CadModule for DrawModule {
                         default: "DIST",
                     }],
                 },
+                RibbonGroup {
+                    title: "Close",
+                    tools: vec![RibbonItem::LargeTool(ToolDef {
+                        id: "BCLOSETESTBLOCK",
+                        label: "Close Test Block",
+                        icon: IconKind::Svg(include_bytes!("../../../assets/icons/mt_ok.svg")),
+                        event: ModuleEvent::Command("BCLOSETESTBLOCK".into()),
+                    })],
+                },
                 // Support group lives on the Start tab now (see view.rs:
                 // start_page_view). Removed from the Draw ribbon to declutter.
             ]

src/modules/draw/modify/block_edit.rs

@@ -119,3 +119,6 @@ inventory::submit!(crate::command::CommandRegistration {
 inventory::submit!(crate::command::CommandRegistration {
     names: &["BSAVE", "BSAVEAS", "BCLOSE"]
 });
+inventory::submit!(crate::command::CommandRegistration {
+    names: &["BTESTBLOCK", "BCLOSETESTBLOCK"]
+});