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/ActionButton.tsx

@@ -0,0 +1,31 @@
+import { Button, type ButtonProps } from "@yaakapp-internal/ui";
+import { useCallback, useState } from "react";
+import type { ActionInvocation } from "@yaakapp-internal/proxy-lib";
+import { useActionMetadata } from "./hooks";
+import { rpc } from "./rpc";
+
+type ActionButtonProps = Omit<ButtonProps, "onClick" | "children"> & {
+  action: ActionInvocation;
+  /** Override the label from metadata */
+  children?: React.ReactNode;
+};
+
+export function ActionButton({ action, children, ...props }: ActionButtonProps) {
+  const meta = useActionMetadata(action);
+  const [busy, setBusy] = useState(false);
+
+  const onClick = useCallback(async () => {
+    setBusy(true);
+    try {
+      await rpc("execute_action", action);
+    } finally {
+      setBusy(false);
+    }
+  }, [action]);
+
+  return (
+    <Button {...props} disabled={props.disabled || busy} isLoading={busy} onClick={onClick}>
+      {children ?? meta?.label ?? "…"}
+    </Button>
+  );
+}