style(why-ci): EN 노트북 YouTube 임베드 셀 hide-input 태그 추가

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Author: Funbucket

book/why_causal_inference/why_causal_inference_en.ipynb

@@ -22,7 +22,11 @@
    "cell_type": "code",
    "execution_count": 2,
    "id": "01f15a40",
-   "metadata": {},
+   "metadata": {
+    "tags": [
+     "hide-input"
+    ]
+   },
    "outputs": [
     {
      "data": {
@@ -1005,4 +1009,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 5
-}
+}