feat: show warning toast when attempting navigation on last or first chapter

src/App.css

@@ -564,6 +564,17 @@ kbd {
   animation: toastFadeIn 0.35s cubic-bezier(0.16, 1, 0.3, 1) forwards;
 }
 
+.chapter-toast.warning-toast {
+  border-color: rgba(245, 158, 11, 0.4);
+  background: rgba(30, 25, 15, 0.92);
+}
+
+.toast-warning-text {
+  color: #fbbf24;
+  font-size: 14px;
+  font-weight: 600;
+}
+
 .toast-badge {
   background: linear-gradient(135deg, #7c3aed, #4f46e5);
   color: #fff;

src/components/MangaViewer.tsx

@@ -83,19 +83,31 @@ export function MangaViewer({
   const [dismissNavError, setDismissNavError] = useState(false);
   const [boundaryWarning, setBoundaryWarning] = useState<'first' | 'last' | null>(null);
   const [dimMap, setDimMap] = useState<Record<string, { width: number; height: number }>>({});
-  const [toast, setToast] = useState<{ title: string; episode: string | null } | null>(null);
+  const [toast, setToast] = useState<{ title?: string; episode?: string | null; text?: string; isWarning?: boolean } | null>(null);
   const toolbarTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const toastTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
   const containerRef = useRef<HTMLDivElement>(null);
 
+  const showNoticeToast = useCallback((text: string, isWarning = true) => {
+    setToast({ text, isWarning });
+    if (toastTimer.current) clearTimeout(toastTimer.current);
+    toastTimer.current = setTimeout(() => {
+      setToast(null);
+    }, 2800);
+  }, []);
+
   // Trigger Chapter Notification Toast on chapter load/change
   useEffect(() => {
     if (!chapter.title) return;
     const parsed = parseTitleAndEpisode(chapter.title);
-    setToast(parsed);
-    const timer = setTimeout(() => {
+    setToast({ title: parsed.title, episode: parsed.episode, isWarning: false });
+    if (toastTimer.current) clearTimeout(toastTimer.current);
+    toastTimer.current = setTimeout(() => {
       setToast(null);
     }, 2800);
-    return () => clearTimeout(timer);
+    return () => {
+      if (toastTimer.current) clearTimeout(toastTimer.current);
+    };
   }, [currentUrl, chapter.title]);
 
   useEffect(() => {
@@ -191,8 +203,10 @@ export function MangaViewer({
       } else {
         setBoundaryWarning('last');
       }
+    } else {
+      showNoticeToast('마지막 화입니다.', true);
     }
-  }, [slotIndex, totalSlots, chapter.next_chapter, boundaryWarning, onNavigate]);
+  }, [slotIndex, totalSlots, chapter.next_chapter, boundaryWarning, onNavigate, showNoticeToast]);
 
   const goPrev = useCallback(() => {
     if (slotIndex > 0) {
@@ -204,8 +218,10 @@ export function MangaViewer({
       } else {
         setBoundaryWarning('first');
       }
+    } else {
+      showNoticeToast('첫 번째 화입니다.', true);
     }
-  }, [slotIndex, chapter.prev_chapter, boundaryWarning, onNavigate]);
+  }, [slotIndex, chapter.prev_chapter, boundaryWarning, onNavigate, showNoticeToast]);
 
   const toggleFullscreen = useCallback(async () => {
     try {
@@ -340,11 +356,17 @@ export function MangaViewer({
         </div>
       )}
 
-      {/* Chapter Transition Toast */}
+      {/* Chapter Transition / Warning Toast */}
       {toast && (
-        <div className="chapter-toast">
-          {toast.episode && <span className="toast-badge">{toast.episode}</span>}
-          <span className="toast-title">{toast.title}</span>
+        <div className={`chapter-toast ${toast.isWarning ? 'warning-toast' : ''}`}>
+          {toast.isWarning ? (
+            <span className="toast-warning-text">⚠️ {toast.text}</span>
+          ) : (
+            <>
+              {toast.episode && <span className="toast-badge">{toast.episode}</span>}
+              {toast.title && <span className="toast-title">{toast.title}</span>}
+            </>
+          )}
         </div>
       )}