Add exact State multiselection, atomic movement and placement Hide

Preserve the desktop-2 captured source (1286 passed, 6 existing ignored). Three menu payload blobs are staged from that verified capture without replacing working files; the strict-lint size correction follows in a separate commit. Native acceptance remains pending.

crates/oa-desktop/src/behavior/state_edit.rs

@@ -25,6 +25,7 @@ pub enum Tool {
 
 #[derive(Debug, Clone)]
 pub enum Event {
+    Selection(crate::app::multiselect::Event),
     Remove(crate::app::diagram_removal::Intent),
     Choose(Tool),
     CreateView(Id),
@@ -38,6 +39,7 @@ pub enum Event {
         context: Context,
         object: Id,
         placement: Option<Id>,
+        selection_target: Option<crate::diagram_usage::Target>,
         anchor: iced::Point,
         bend: Option<usize>,
         route_segment: Option<(usize, Position)>,
@@ -101,7 +103,8 @@ impl Event {
     pub fn context(&self) -> Option<Context> {
         match self {
             Self::Remove(intent) => Some(intent.context),
-            Self::Choose(_) | Self::CreateView(_) => None,
+            // Group events carry their own exact selection envelope.
+            Self::Selection(_) | Self::Choose(_) | Self::CreateView(_) => None,
             Self::Select(c, _)
             | Self::Pan(c, _)
             | Self::Zoom(c, _)