Move Tree component to @yaakapp-internal/ui package

Decouple Tree from client app's hotkey system by adding
getSelectedItems() to TreeHandle and having callers register
hotkeys externally. Extract shared action callbacks to eliminate
duplication between hotkey and context menu handlers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/ui/src/components/tree/context.ts

@@ -0,0 +1,60 @@
+import type { WritableAtom } from 'jotai';
+import { useAtomValue, useStore } from 'jotai';
+import { selectAtom } from 'jotai/utils';
+import { createContext, useCallback, useContext, useMemo } from 'react';
+
+type CollapsedMap = Record<string, boolean>;
+type SetAction = CollapsedMap | ((prev: CollapsedMap) => CollapsedMap);
+export type CollapsedAtom = WritableAtom<CollapsedMap, [SetAction], void>;
+
+export const CollapsedAtomContext = createContext<CollapsedAtom | null>(null);
+
+export function useCollapsedAtom(): CollapsedAtom {
+  const atom = useContext(CollapsedAtomContext);
+  if (!atom) throw new Error('CollapsedAtomContext not provided');
+  return atom;
+}
+
+export function useIsCollapsed(itemId: string | undefined) {
+  const collapsedAtom = useCollapsedAtom();
+  const derivedAtom = useMemo(
+    () => selectAtom(collapsedAtom, (map) => !!map[itemId ?? 'n/a'], Object.is),
+    [collapsedAtom, itemId],
+  );
+  return useAtomValue(derivedAtom);
+}
+
+export function useSetCollapsed(itemId: string | undefined) {
+  const collapsedAtom = useCollapsedAtom();
+  const store = useStore();
+  return useCallback(
+    (next: boolean | ((prev: boolean) => boolean)) => {
+      const key = itemId ?? 'n/a';
+      const prevMap = store.get(collapsedAtom);
+      const prevValue = !!prevMap[key];
+      const value = typeof next === 'function' ? next(prevValue) : next;
+      if (value === prevValue) return;
+      store.set(collapsedAtom, { ...prevMap, [key]: value });
+    },
+    [collapsedAtom, itemId, store],
+  );
+}
+
+export function useCollapsedMap() {
+  const collapsedAtom = useCollapsedAtom();
+  return useAtomValue(collapsedAtom);
+}
+
+export function useIsAncestorCollapsed(ancestorIds: string[]) {
+  const collapsedAtom = useCollapsedAtom();
+  const derivedAtom = useMemo(
+    () =>
+      selectAtom(
+        collapsedAtom,
+        (collapsed) => ancestorIds.some((id) => collapsed[id]),
+        (a, b) => a === b,
+      ),
+    [collapsedAtom, ancestorIds],
+  );
+  return useAtomValue(derivedAtom);
+}