feat: add Sequencer navigation item to AppSidebar and wrap SequencerPage in AppLayout for improved structure

src/components/AppSidebar.tsx

@@ -15,6 +15,7 @@ import {
   PlayCircle,
   Settings,
   Users,
+  AudioLines,
 } from 'lucide-react'
 import { CreditsNav } from './nav/CreditsNav'
 import { NavGroup } from './nav/NavGroup'
@@ -48,6 +49,7 @@ export function AppSidebar({ showCompactPlayer = false }: AppSidebarProps) {
           <NavItem href="/" icon={Home} title="Dashboard" />
           <NavItem href="/sounds" icon={Music} title="Sounds" />
           <NavItem href="/playlists" icon={PlayCircle} title="Playlists" />
+          <NavItem href="/sequencer" icon={AudioLines} title="Sequencer" />
           <NavItem href="/extractions" icon={Download} title="Extractions" />
           <NavItem href="/schedulers" icon={CalendarClock} title="Schedulers" />
         </NavGroup>