feat(block-editor): add Save Block As

Create a new named definition from current session edits, restore the source checkpoint, and continue editing the copy with fresh local history. Add the name dialog and Save dropdown, clone supported owned metadata onto independent handles, and refuse unsupported relationships atomically.

src/app/mod.rs

@@ -9,6 +9,7 @@ pub(crate) mod config;
 pub use automation::{export_headless, serve};
 mod annotation_data;
 mod block_editor;
+mod block_save_as;
 #[cfg(test)]
 mod block_editor_tests;
 mod command_driver;
@@ -570,6 +571,7 @@ pub(super) struct OpenCADStudio {
     drawing_units: Option<crate::ui::window::drawing_units::State>,
     /// Working copy of the Block Definition dialog; `None` while it is closed.
     block_definition: Option<crate::ui::window::block_definition::BlockDefinitionState>,
+    block_save_as: Option<crate::ui::window::block_save_as::State>,
     /// PDF dialogs' working copies; `None` while closed.
     pdf_attach: Option<crate::ui::window::pdf_dialogs::PdfAttachState>,
     point_cloud_attach: Option<crate::ui::window::pdf_dialogs::PointCloudAttachState>,
@@ -2177,6 +2179,7 @@ pub enum ModalKind {
     DimStyle,
     Unsaved,
     BlockEditChanges,
+    BlockSaveAs,
     SaveDialog,
     Recovery,
     /// Fonts referenced by the drawing are missing on this machine.
@@ -2807,6 +2810,8 @@ pub enum Message {
     BlockEditChangesSave,
     BlockEditChangesDiscard,
     BlockEditChangesCancel,
+    BlockSaveAsName(String),
+    BlockSaveAsApply,
     // ── AEC / unsupported-object drop warning (lossy Save-As) ──────────────
     /// Save as the source DWG version so the unsupported objects survive.
     AecDropSameVersion,
@@ -4551,6 +4556,7 @@ impl OpenCADStudio {
             layer_translator: None,
             drawing_units: None,
             block_definition: None,
+            block_save_as: None,
             pdf_attach: None,
             point_cloud_attach: None,
             attdef_dialog: None,