fix: closing-segment markers on closed polylines; case-insensitive page-setup names

- resolve_point, set_polyline_vertex and the solver's point_for_marker
  treat the marker one past the last vertex of a closed polyline as
  vertex 0, the way line_segment already did. Equal (#1366), the axis
  pre-alignment (#1365) and the transform pin (#1361) address a picked
  segment's end that way, so on the closing segment they either refused
  the pick or pinned nothing.
- Page-setup dictionary keys compare case-insensitively: page_setup_save
  replaces "site" when "Site" exists instead of adding a second entry
  (PSETUPIN counted it as replaced, #1344), delete and rename match the
  same way, and a rename that only changes case is allowed.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/scene/page_setup.rs

@@ -175,7 +175,23 @@ impl Scene {
         let ObjectType::Dictionary(d) = self.document.objects.get(&dh)? else {
             return None;
         };
-        d.entries.iter().find(|(k, _)| k == name).map(|(_, h)| *h)
+        d.entries
+            .iter()
+            .find(|(k, _)| k.eq_ignore_ascii_case(name))
+            .map(|(_, h)| *h)
+    }
+
+    /// The dictionary's own spelling of `name` (page-setup names compare
+    /// case-insensitively, like every named-object dictionary key).
+    fn page_setup_key(&self, name: &str) -> Option<String> {
+        let dh = self.plotsettings_dict_handle()?;
+        let ObjectType::Dictionary(d) = self.document.objects.get(&dh)? else {
+            return None;
+        };
+        d.entries
+            .iter()
+            .find(|(k, _)| k.eq_ignore_ascii_case(name))
+            .map(|(k, _)| k.clone())
     }
 
     /// Create or update the named page setup from `ps` (its `page_name` and
@@ -183,7 +199,9 @@ impl Scene {
     /// are inserted and registered in the dictionary.
     pub fn page_setup_save(&mut self, name: &str, mut ps: PlotSettings) {
         let dict_handle = self.ensure_plotsettings_dict();
-        ps.page_name = name.to_string();
+        // Replacing keeps the entry's stored spelling so the dictionary key
+        // and the object's page_name stay one name.
+        ps.page_name = self.page_setup_key(name).unwrap_or_else(|| name.to_string());
         ps.owner = dict_handle;
         if let Some(h) = self.page_setup_handle(name) {
             ps.handle = h;
@@ -206,8 +224,12 @@ impl Scene {
         let handle = if let Some(ObjectType::Dictionary(d)) =
             self.document.objects.get_mut(&dict_handle)
         {
-            let h = d.entries.iter().find(|(k, _)| k == name).map(|(_, h)| *h);
-            d.entries.retain(|(k, _)| k != name);
+            let h = d
+                .entries
+                .iter()
+                .find(|(k, _)| k.eq_ignore_ascii_case(name))
+                .map(|(_, h)| *h);
+            d.entries.retain(|(k, _)| !k.eq_ignore_ascii_case(name));
             h
         } else {
             None
@@ -223,7 +245,8 @@ impl Scene {
         if old == new || new.trim().is_empty() {
             return;
         }
-        if self.page_setup_handle(new).is_some() {
+        // A different spelling of the same name is a rename, not a collision.
+        if !old.eq_ignore_ascii_case(new) && self.page_setup_handle(new).is_some() {
             return; // name collision
         }
         let Some(dict_handle) = self.plotsettings_dict_handle() else {
@@ -231,7 +254,7 @@ impl Scene {
         };
         let mut renamed = None;
         if let Some(ObjectType::Dictionary(d)) = self.document.objects.get_mut(&dict_handle) {
-            if let Some(e) = d.entries.iter_mut().find(|(k, _)| k == old) {
+            if let Some(e) = d.entries.iter_mut().find(|(k, _)| k.eq_ignore_ascii_case(old)) {
                 e.0 = new.to_string();
                 renamed = Some(e.1);
             }