feat: two-finger long-press opens the panel

A second way in that does not depend on finding a 7px tab. Two fingers rather
than one because Chromium claims the one-finger long press for image menus and
text selection, and a manga reader is all images. Passive listeners; a
pinch-zoom cancels via the 15px slop check.

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

userscript/manga-bookmark.user.js

@@ -1200,6 +1200,71 @@
     setInterval(fire, 1500); // catch routes that bypass history
   }
 
+  // ============================================================
+  // Two-finger long-press — a way in that does not depend on finding a 7px tab
+  //
+  // Deliberately two fingers, not one: Chromium claims the one-finger long
+  // press for image context menus, text selection, and link previews, and on a
+  // manga reader the whole viewport is images. It assigns no two-finger long
+  // press, so these listeners stay passive and never preventDefault.
+  // ============================================================
+
+  const LONGPRESS_MS = 500;
+  const LONGPRESS_SLOP = 15; // px either finger may drift before it counts as a drag
+
+  function installLongPress() {
+    let timer = null;
+    let start = null; // [{x, y}, {x, y}] — where each finger landed
+
+    const cancel = () => {
+      if (timer) clearTimeout(timer);
+      timer = null;
+      start = null;
+    };
+
+    const opts = { passive: true, capture: true };
+
+    // Fires once per finger, so the first touch cancels and the second arms.
+    // A third finger cancels again.
+    document.addEventListener(
+      "touchstart",
+      (e) => {
+        cancel();
+        if (e.touches.length !== 2) return;
+        start = [
+          { x: e.touches[0].clientX, y: e.touches[0].clientY },
+          { x: e.touches[1].clientX, y: e.touches[1].clientY },
+        ];
+        timer = setTimeout(() => {
+          cancel();
+          togglePanel();
+        }, LONGPRESS_MS);
+      },
+      opts
+    );
+
+    // A pinch-zoom is two fingers held down, so the slop check is what keeps it
+    // from opening the panel mid-gesture.
+    document.addEventListener(
+      "touchmove",
+      (e) => {
+        if (!start || e.touches.length !== 2) return cancel();
+        for (let i = 0; i < 2; i++) {
+          if (
+            Math.abs(e.touches[i].clientX - start[i].x) > LONGPRESS_SLOP ||
+            Math.abs(e.touches[i].clientY - start[i].y) > LONGPRESS_SLOP
+          ) {
+            return cancel();
+          }
+        }
+      },
+      opts
+    );
+
+    document.addEventListener("touchend", cancel, opts);
+    document.addEventListener("touchcancel", cancel, opts);
+  }
+
   // ============================================================
   // Boot
   // ============================================================
@@ -1209,6 +1274,7 @@
     state.page = detect();
     render();
     installNavWatcher();
+    installLongPress();
     window.addEventListener("online", drain); // signal returned while the page stayed open
     // Sync first: both auto-record and the latest-chapter checks below need to
     // know which series are bookmarked and how fresh they are.