fix: replace {#await} IIFE trick with $effect for streamed data on discover page

The {#await ... then} + {@const} IIFE pattern for assigning to $state
variables stopped working reliably in Svelte 5.53+. Replaced with a
proper $effect that awaits both streamed promises and assigns to state,
which correctly triggers reactivity.

Also: switch library page selection mode entry from long-press to a
'Select' button in the page header.

ui/src/routes/books/+page.svelte

@@ -53,11 +53,6 @@
 		filteredBooks.length > 0 && filteredBooks.every((b) => selected.has(b.slug))
 	);
 
-	function enterSelectMode(slug: string) {
-		selectMode = true;
-		selected = new Set([slug]);
-	}
-
 	function exitSelectMode() {
 		selectMode = false;
 		selected = new Set();
@@ -81,43 +76,11 @@
 		}
 	}
 
-	// Long-press support (pointer events, works on desktop + mobile)
-	let longPressTimer: ReturnType<typeof setTimeout> | null = null;
-	let longPressFired = false;
-
-	function onPointerDown(slug: string) {
-		if (selectMode) return;
-		longPressFired = false;
-		longPressTimer = setTimeout(() => {
-			longPressFired = true;
-			enterSelectMode(slug);
-		}, 500);
-	}
-
-	function onPointerUp() {
-		if (longPressTimer) {
-			clearTimeout(longPressTimer);
-			longPressTimer = null;
-		}
-	}
-
-	function onPointerCancel() {
-		if (longPressTimer) {
-			clearTimeout(longPressTimer);
-			longPressTimer = null;
-		}
-	}
-
-	// Prevent navigation click if long-press just fired
+	// Card click: in selection mode, toggle selection; otherwise navigate normally
 	function onCardClick(e: MouseEvent, slug: string) {
 		if (selectMode) {
 			e.preventDefault();
 			toggleSelect(slug);
-			return;
-		}
-		if (longPressFired) {
-			e.preventDefault();
-			longPressFired = false;
 		}
 	}
 
@@ -175,6 +138,14 @@
 		>
 			Cancel
 		</button>
+	{:else if data.books?.length}
+		<button
+			type="button"
+			onclick={() => { selectMode = true; }}
+			class="text-sm text-(--color-muted) hover:text-(--color-text) transition-colors pt-1"
+		>
+			Select
+		</button>
 	{/if}
 </div>
 
@@ -228,9 +199,6 @@
 			<a
 				href="/books/{book.slug}"
 				onclick={(e) => onCardClick(e, book.slug)}
-				onpointerdown={() => onPointerDown(book.slug)}
-				onpointerup={onPointerUp}
-				onpointercancel={onPointerCancel}
 				draggable="false"
 				class="group relative flex flex-col rounded-lg overflow-hidden bg-(--color-surface-2) border transition-colors select-none
 					{isSelected

ui/src/routes/discover/+page.svelte

@@ -60,10 +60,17 @@
 		try { return JSON.parse(genres) as string[]; } catch { return []; }
 	}
 
-	// Resolved books from streamed promise (populated in {#await} block via binding trick)
+	// Resolved books from streamed promises — populated via $effect once promises settle
 	let resolvedBooks = $state<Book[]>([]);
 	let resolvedVotedBooks = $state<VotedBook[]>([]);
 
+	$effect(() => {
+		Promise.all([data.streamed.books, data.streamed.votedBooks]).then(([books, vb]) => {
+			resolvedBooks = books as Book[];
+			resolvedVotedBooks = vb as VotedBook[];
+		});
+	});
+
 	let deck = $derived.by(() => {
 		let books = resolvedBooks;
 		if (prefs.onboarded && prefs.genres.length > 0) {
@@ -479,12 +486,6 @@
 </div>
 {/if}
 
-<!-- ── Await streamed data ─────────────────────────────────────────────────────── -->
-{#await Promise.all([data.streamed.books, data.streamed.votedBooks]) then [books, vb]}
-	<!-- Silently populate reactive state once data resolves -->
-	{@const _ = (() => { resolvedBooks = books as Book[]; resolvedVotedBooks = vb as VotedBook[]; return ''; })()}
-{/await}
-
 <!-- ── Page layout ────────────────────────────────────────────────────────────── -->
 <div class="select-none -mx-4 -my-8 lg:min-h-[calc(100svh-3.5rem)]
 	lg:grid lg:grid-cols-[1fr_380px] xl:grid-cols-[1fr_420px]">