REFEDIT: Edit Reference dialog and unique names for xref objects

REFEDIT opens a dialog after the pick: the nesting chain as chips with a
preview of the chosen definition, all objects or picking them in the
drawing, attribute definitions (offered only when the definition has
them), locking objects outside the working set and unique names for an
external reference's named objects. The settings are remembered.

With unique names an xref's dependent layers, linetypes, text styles and
blocks are checked out as $N$NAME records of their own; without, under
the plain name, sharing a host record of that name. Save writes them back
under the reference's names, and the records made for the session are
removed when it closes. -REFEDIT uses the remembered settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/settings.rs

@@ -652,6 +652,9 @@ pub struct UserSettings {
     /// BLOCKNAVIGATE (default ".").
     #[serde(default = "default_block_navigate")]
     pub block_navigate: String,
+    /// The Edit Reference dialog's settings.
+    #[serde(default)]
+    pub refedit: RefEditOptions,
     /// XFADECTL: how far objects outside the REFEDIT working set fade (0–90, default 70).
     #[serde(default = "default_xfadectl")]
     pub xfadectl: u8,
@@ -687,6 +690,30 @@ pub struct PaletteBlockRef {
     pub drawing: bool,
 }
 
+/// The Edit Reference dialog's settings, remembered between sessions: give
+/// an external reference's clashing named objects unique names, check out
+/// attribute definitions, lock what is outside the working set, pick the
+/// working set's objects in the drawing.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct RefEditOptions {
+    pub unique_names: bool,
+    pub attributes: bool,
+    pub lock: bool,
+    pub nested: bool,
+}
+
+impl Default for RefEditOptions {
+    fn default() -> Self {
+        Self {
+            unique_names: true,
+            attributes: false,
+            lock: true,
+            nested: false,
+        }
+    }
+}
+
 /// The Blocks palette's insertion options.
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 pub struct BlockInsertOptions {
@@ -938,6 +965,7 @@ impl Default for UserSettings {
             block_mru_list: 50,
             block_redefine_mode: 1,
             block_navigate: ".".to_string(),
+            refedit: RefEditOptions::default(),
             xfadectl: 70,
             count_color: 3,
             count_error_color: 1,