feat: add themeable design tokens with cookie-backed SSR

frontend/src/routes/(root)/+layout.svelte

@@ -8,17 +8,36 @@
 	import { setBookOperationsState } from '$lib/state/bookOperations.svelte';
 	import { setBookshelfState } from '$lib/state/bookshelf.svelte';
 	import { setLibraryState } from '$lib/state/library.svelte.js';
+	import { setThemeState } from '$lib/theme/theme.svelte';
+	import type { ThemeConfig } from '$lib/theme/presets';
 
 	import { ModeWatcher } from 'mode-watcher';
-	import type { Snippet } from 'svelte';
+	import { untrack, type Snippet } from 'svelte';
 	import { Toaster } from 'svelte-sonner';
 
-	let { data, children }: { data: { libraries: PaginatedResponse<Library> }; children: Snippet } =
-		$props();
+	let {
+		data,
+		children
+	}: {
+		data: { libraries: PaginatedResponse<Library>; theme: ThemeConfig; user: { email: string } };
+		children: Snippet;
+	} = $props();
 
-	const libraryState = setLibraryState(data.libraries.items);
+	// These states are seeded once and then own their own data — LibraryState has
+	// updateLibraries() for later syncing, and ThemeState owns the config after
+	// init. `untrack` says that explicitly, instead of silently capturing the
+	// initial value and warning about it.
+	const libraryState = setLibraryState(untrack(() => data.libraries.items));
 	const bookshelfState = setBookshelfState();
 	const bookOps = setBookOperationsState(libraryState.activeLibrary!.id);
+	const theme = setThemeState(untrack(() => data.theme));
+
+	// Inline custom properties live on :root and so are mode-blind. When the
+	// light/dark switch flips, rewrite them for the mode now showing.
+	$effect(() => {
+		theme.mode;
+		theme.syncMode();
+	});
 </script>
 
 <Toaster />
@@ -27,7 +46,7 @@
 <div class="[--header-height:calc(--spacing(14))]">
 	<Sidebar.Provider class="flex flex-col">
 		<div class="flex h-screen">
-			<AppSidebar />
+			<AppSidebar user={data.user} />
 			<Sidebar.Inset class="flex min-w-0 flex-1 flex-col overflow-x-hidden">
 				<SiteHeader />
 				<div class="mt-4 flex-1 overflow-hidden p-4 pt-0">