feat(vue/primitives): add FocusScope component with auto-focus and focus trap functionality

vue/primitives/src/focus-scope/stack.ts

@@ -0,0 +1,29 @@
+export interface FocusScopeAPI {
+  paused: boolean;
+  pause: () => void;
+  resume: () => void;
+}
+
+const stack: FocusScopeAPI[] = [];
+
+export function createFocusScopesStack() {
+  return {
+    add(focusScope: FocusScopeAPI) {
+      const current = stack.at(-1);
+      if (focusScope !== current) current?.pause();
+
+      // Remove if already in stack (deduplicate), then push to top
+      const index = stack.indexOf(focusScope);
+      if (index !== -1) stack.splice(index, 1);
+
+      stack.push(focusScope);
+    },
+
+    remove(focusScope: FocusScopeAPI) {
+      const index = stack.indexOf(focusScope);
+      if (index !== -1) stack.splice(index, 1);
+
+      stack.at(-1)?.resume();
+    },
+  };
+}