Checkpoint source 7 workflows and in-progress diagram authoring redesign

Preserve current core, source, REST, desktop, recovery, documentation and validation work, including AGENTS.md and the development summary. This is a work-in-progress checkpoint: the new compact palette has outstanding compilation errors and native acceptance; earlier passing gates retain their documented scope.

crates/oa-desktop/src/diagram/pointer_tests.rs

@@ -70,6 +70,7 @@ fn canvas(app: &App, zoom: f32) -> DiagramCanvas<'_> {
         context: app.route_context().unwrap(),
         selected_bend: None,
         editable: true,
+        placing: false,
         connection: app.connection.as_ref(),
     }
 }