feat(web): collapse reader toc/bookmark buttons into single 导航 toolbar button

frontend/src/readers/TextReader.tsx

@@ -192,7 +192,7 @@ function MdView({ book, initialLocator, initialPercent, chrome }: ReaderProps) {
             aria-controls="reader-nav"
             onClick={() => setNav((v) => !v)}
           >
-            书签
+            导航
           </button>
         </ReaderSheet>
       )}
@@ -311,22 +311,14 @@ function TxtView({ book, initialLocator, initialPercent, chrome }: ReaderProps)
         <ReaderSheet pr={pr} frac={total} onSeek={seek}>
           <button
             className="rd-btn"
-            aria-expanded={nav === "bm"}
+            aria-expanded={!!nav}
             aria-controls="reader-nav"
-            onClick={() => setNav(nav === "bm" ? null : "bm")}
+            onClick={() => setNav(nav ? null : chapters.length > 1 ? "toc" : "bm")}
           >
-            书签
+            导航
           </button>
           {chapters.length > 1 && (
             <>
-              <button
-                className="rd-btn"
-                aria-expanded={nav === "toc"}
-                aria-controls="reader-nav"
-                onClick={() => setNav(nav === "toc" ? null : "toc")}
-              >
-                目录
-              </button>
               <span className="text-xs opacity-60 tabular-nums">
                 {ci + 1}/{chapters.length}
               </span>