feat(ui): add AppHeader support to 404 not-found page

app/(app)/not-found.tsx

@@ -3,27 +3,30 @@
  * @description Server component rendering a custom 404 page for missing or invalid routes within the app layout.
  */
 
+import { AppHeader } from "@/components/layout/AppHeader";
 import { AlertCircle } from "lucide-react";
 
 /** Renders the 404 Not Found fallback view containing an alert icon, message, and navigation link back to the summary page. */
 export default function NotFound() {
   return (
-    <div className="flex flex-col items-center justify-center h-full w-full text-center my-auto">
-      <div className="max-w-md w-full space-y-6">
-        {/* Icon Badge */}
-        <div className="mx-auto w-16 h-16 rounded-2xl bg-destructive-bg border border-destructive-border flex items-center justify-center text-destructive shadow-sm">
-          <AlertCircle size={36} />
-        </div>
+    <div className="flex flex-col h-full w-full bg-background p-4 min-h-0 overflow-hidden">
+      <AppHeader isNotFound />
+      <div className="flex flex-col items-center justify-center h-full w-full text-center my-auto">
+        <div className="max-w-md w-full space-y-6">
+          {/* Icon Badge */}
+          <div className="mx-auto w-16 h-16 rounded-2xl bg-destructive-bg border border-destructive-border flex items-center justify-center text-destructive shadow-sm">
+            <AlertCircle size={36} />
+          </div>
 
-        {/* Text Content */}
-        <div className="space-y-2">
-          <h1 className="text-2xl font-bold tracking-tight text-foreground">
-            Page not found
-          </h1>
-          <p className="text-sm text-foreground-muted leading-relaxed">
-            The page you are looking for doesn't exist or has been moved. Please
-            check the URL or head back to your summary.
-          </p>
+          {/* Text Content */}
+          <div className="space-y-2">
+            <h1 className="text-2xl font-bold tracking-tight text-foreground">
+              Page not found
+            </h1>
+            <p className="text-sm text-foreground-muted leading-relaxed">
+              The page you are looking for doesn't exist or has been moved.
+            </p>
+          </div>
         </div>
       </div>
     </div>

components/layout/AppHeader.tsx

@@ -1,6 +1,6 @@
 /**
  * @file components/layout/AppHeader.tsx
- * @description Application top header component providing navigation controls, dynamic channel or friend tab titles, optional server settings, member list toggles, and legal views support.
+ * @description Application top header component providing navigation controls, dynamic channel or friend tab titles, optional server settings, member list toggles, legal views, and 404 support.
  */
 
 "use client";
@@ -14,6 +14,7 @@ import {
   Settings,
   FileText,
   ShieldCheck,
+  AlertCircle,
 } from "lucide-react";
 import { ServerSettingsMenu } from "./ServerSettingsMenu";
 import { FriendsHeader, TabType } from "@/components/friends/FriendsHeader";
@@ -35,9 +36,10 @@ interface AppHeaderProps {
   isSettings?: boolean;
   isLegalImprint?: boolean;
   isLegalPrivacy?: boolean;
+  isNotFound?: boolean;
 }
 
-/** Renders the application header with navigation controls, dynamic titles, tabs, and action buttons. */
+/** Renders the application header with navigation controls, dynamic titles, tabs, action buttons, and 404 support. */
 export function AppHeader({
   title,
   showMembersButton = false,
@@ -50,6 +52,7 @@ export function AppHeader({
   isSettings = false,
   isLegalImprint = false,
   isLegalPrivacy = false,
+  isNotFound = false,
 }: AppHeaderProps) {
   const { isNavOpen, toggleNav, toggleMembers } = useSidebarStore();
 
@@ -62,7 +65,8 @@ export function AppHeader({
     !!server ||
     showFriendsTabs ||
     isSettings ||
-    isLegalView;
+    isLegalView ||
+    isNotFound;
 
   return (
     <div
@@ -87,6 +91,16 @@ export function AppHeader({
           )}
         </button>
 
+        {/* 404 Not Found Header Title */}
+        {isNotFound && (
+          <div className="flex items-center gap-1.5 ml-1 min-w-0">
+            <AlertCircle className="w-4 h-4 text-destructive shrink-0" />
+            <h1 className="font-bold text-white text-base truncate">
+              Not Found
+            </h1>
+          </div>
+        )}
+
         {/* Settings View Header Title */}
         {isSettings && (
           <div className="flex items-center gap-1.5 ml-1 min-w-0">
@@ -116,7 +130,7 @@ export function AppHeader({
         )}
 
         {/* Dynamic Channel Title */}
-        {!isSettings && !isLegalView && title && (
+        {!isSettings && !isLegalView && !isNotFound && title && (
           <div className="flex items-center gap-1.5 ml-1 min-w-0">
             <Hash className="w-4 h-4 text-muted shrink-0" />
             <h1 className="font-bold text-white text-base truncate">{title}</h1>
@@ -126,6 +140,7 @@ export function AppHeader({
         {/* Friends Header Component */}
         {!isSettings &&
           !isLegalView &&
+          !isNotFound &&
           showFriendsTabs &&
           setActiveTab &&
           activeTab && (