chore: move App and app related code to app layer

src/app/ui/Layout.svelte

@@ -0,0 +1,32 @@
+<script lang="ts">
+import favicon from '$shared/assets/favicon.svg';
+import * as Sidebar from '$shared/shadcn/ui/sidebar/index';
+import { AppSidebar } from '$widgets/AppSidebar';
+
+let { children } = $props();
+</script>
+
+<svelte:head>
+    <link rel="icon" href={favicon} />
+</svelte:head>
+
+<div class="app">
+    <header></header>
+
+    <Sidebar.Provider>
+        <AppSidebar />
+        <main>
+            <Sidebar.Trigger />
+            {@render children?.()}
+        </main>
+    </Sidebar.Provider>
+
+    <footer></footer>
+</div>
+
+<style>
+#app-root {
+    width: 100%;
+    height: 100vh;
+}
+</style>