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>

apps/yaak-proxy/hooks.ts

@@ -0,0 +1,35 @@
+import { useEffect, useState } from "react";
+import type {
+  ActionInvocation,
+  ActionMetadata,
+} from "@yaakapp-internal/proxy-lib";
+import { rpc } from "./rpc";
+
+let cachedActions: [ActionInvocation, ActionMetadata][] | null = null;
+
+/** Fetch and cache all action metadata. */
+async function getActions(): Promise<[ActionInvocation, ActionMetadata][]> {
+  if (!cachedActions) {
+    const { actions } = await rpc("list_actions", {});
+    cachedActions = actions;
+  }
+  return cachedActions;
+}
+
+/** Look up metadata for a specific action invocation. */
+export function useActionMetadata(
+  action: ActionInvocation,
+): ActionMetadata | null {
+  const [meta, setMeta] = useState<ActionMetadata | null>(null);
+
+  useEffect(() => {
+    getActions().then((actions) => {
+      const match = actions.find(
+        ([inv]) => inv.scope === action.scope && inv.action === action.action,
+      );
+      setMeta(match?.[1] ?? null);
+    });
+  }, [action]);
+
+  return meta;
+}