feat: resizable sidebar

Co-Authored-By: ALiNew <42788336+sukjinkim@users.noreply.github.com>

src/lib/components/channel/Channel.svelte

@@ -290,7 +290,7 @@
 
 <div
 	class="h-screen max-h-[100dvh] transition-width duration-200 ease-in-out {$showSidebar
-		? 'md:max-w-[calc(100%-260px)]'
+		? 'md:max-w-[calc(100%-var(--sidebar-width))]'
 		: ''} w-full max-w-full flex flex-col"
 	id="channel-container"
 >