Fix mark-watched button crash on channel videos tab (#247)

On channel pages, #video-title's parent element is deeply nested inside
#dismissible > #details > #meta > h3 > a, not a direct child of the
button container. This caused insertBefore to throw "Child to insert
before is not a child of this node". Now checks if the reference node
is a direct child first, and falls back to inserting into #meta area.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: OsaSoft

videos/SubscriptionsVideo.js

@@ -79,7 +79,18 @@ class SubscriptionVideo extends Video {
             }
         } else {
             // Old layout: insert before title area
-            buttonContainer.insertBefore(container, buttonContainer.querySelector("#video-title")?.parentElement || buttonContainer.firstChild);
+            let refNode = buttonContainer.querySelector("#video-title")?.parentElement;
+            if (refNode?.parentElement !== buttonContainer) {
+                // Channel page layout: #video-title is deeply nested, insert into #meta area
+                let metaDiv = buttonContainer.querySelector("#meta");
+                if (metaDiv) {
+                    metaDiv.appendChild(container);
+                } else {
+                    buttonContainer.appendChild(container);
+                }
+            } else {
+                buttonContainer.insertBefore(container, refNode || buttonContainer.firstChild);
+            }
         }
     }
 }