feat(ui): right-edge side toolbar; drop the paper-space ribbon tab

Switching to a paper layout used to hijack the ribbon with a contextual
"Layout" tab. Replace that with a reusable right-edge vertical toolbar:
a single centred column of icon buttons floated over the canvas, built
from a flat ToolDef list and dispatching through the existing
RibbonToolClick path (ui::side_toolbar). Paper space now shows Viewport /
Page Setup / Export PDF there and leaves the ribbon on the user's tab;
the contextual layout tab and its three auto-switch hooks are removed.
The toolbar is generic infrastructure for future context action sets.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/update.rs

@@ -5005,13 +5005,9 @@ impl OpenCADStudio {
                 self.tabs[i].scene.deselect_all();
                 self.tabs[i].scene.restore_saved_camera();
                 self.tabs[i].last_synced_camera_gen = self.tabs[i].scene.camera_generation;
-                if going_to_paper {
-                    if let Some(idx) = self.ribbon.layout_module_index() {
-                        self.ribbon.select(idx);
-                    }
-                } else if self.ribbon.active_is_layout() {
-                    self.ribbon.select(0);
-                }
+                // Paper-space tools live in the right-edge side toolbar now, so
+                // entering/leaving a layout no longer hijacks the ribbon tab.
+                let _ = going_to_paper;
                 // Refresh VP freeze columns for the new layout.
                 let doc_layers = self.tabs[i].scene.document.layers.clone();
                 let vp_info = self.tabs[i].scene.viewport_list();
@@ -5054,9 +5050,6 @@ impl OpenCADStudio {
                         self.tabs[i].scene.ensure_sheet_viewport(&new_name);
                         self.tabs[i].scene.deselect_all();
                         self.tabs[i].scene.fit_all();
-                        if let Some(idx) = self.ribbon.layout_module_index() {
-                            self.ribbon.select(idx);
-                        }
                         self.command_line.push_output(&format!(
                             "Layout \"{new_name}\" created — use MVIEW to add a viewport"
                         ));
@@ -5075,12 +5068,6 @@ impl OpenCADStudio {
                 if self.tabs[i].scene.delete_layout(&name) {
                     self.layout_context_menu = None;
                     self.layout_rename_state = None;
-                    // If we fell back to Model space, update ribbon.
-                    if self.tabs[i].scene.current_layout == "Model"
-                        && self.ribbon.active_is_layout()
-                    {
-                        self.ribbon.select(0);
-                    }
                     self.command_line
                         .push_output(&format!("Layout \"{name}\" silindi"));
                     self.tabs[i].dirty = true;

src/app/view.rs

@@ -1119,6 +1119,16 @@ impl OpenCADStudio {
             }
         }
 
+        // Paper-space context actions: a right-edge vertical toolbar
+        // (viewport / page setup / plot) instead of a contextual ribbon tab.
+        if is_paper && !tab.is_start {
+            if let Some(tb) = crate::ui::side_toolbar::view(
+                &crate::modules::layout::paper_space_tools(),
+            ) {
+                viewport_stack = viewport_stack.push(tb);
+            }
+        }
+
         // Quick Properties: compact floating property panel on selection,
         // anchored at the canvas top-left so it doesn't track the cursor.
         if self.quick_properties && !tab.is_start {