docs: correct the long-press comment's pinch-zoom claim

The slop check cancels a normal-speed pinch, not every pinch. Verified live:
a deliberately slow one that stays inside 15px for the full 500ms does open
the panel. Accepted — an absolute per-finger drift threshold cannot separate
that from two fingers resting, which is the gesture being detected.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

userscript/manga-bookmark.user.js

@@ -1243,8 +1243,13 @@
       opts
     );
 
-    // A pinch-zoom is two fingers held down, so the slop check is what keeps it
+    // A pinch-zoom is two fingers held down, so the slop check is what keeps a
-    // from opening the panel mid-gesture.
+    // normal-speed one from opening the panel mid-gesture. Verified 2026-07-28:
+    // a pinch that reaches 240px in ~240ms cancels well before the timer. A
+    // deliberately slow pinch that stays inside the slop for the full 500ms
+    // does open the panel — accepted, since an absolute per-finger drift
+    // threshold cannot tell that apart from two fingers resting, which is the
+    // gesture this is for.
     document.addEventListener(
       "touchmove",
       (e) => {