perf: cache home stats + ratings, fix discover card pop animation

Cache home stats (10 min) and recently added books (5 min) to avoid
hitting PocketBase on every homepage load. Cache all ratings for
discovery ranking (5 min) with invalidation on setBookRating.
invalidateBooksCache now clears all related keys atomically.

Fix discover card pop-to-full-size bug: new card now transitions from
scale(0.95) to scale(1.0) matching its back-card position, instead of
snapping to full size instantly after each swipe.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -130,7 +130,43 @@
 
 	let cardEl = $state<HTMLDivElement | null>(null);
 
+	// ── Card entry animation (prevents pop-to-full-size after swipe) ─────────────
+	let cardEntering = $state(false);
+	let entryTransition = $state(false);
+	let entryCleanup: ReturnType<typeof setTimeout> | null = null;
+
+	function startEntryAnimation() {
+		if (entryCleanup) clearTimeout(entryCleanup);
+		cardEntering = true;
+		entryTransition = true;
+		requestAnimationFrame(() => {
+			cardEntering = false;
+			entryCleanup = setTimeout(() => { entryTransition = false; }, 400);
+		});
+	}
+
+	function cancelEntryAnimation() {
+		if (entryCleanup) { clearTimeout(entryCleanup); entryCleanup = null; }
+		cardEntering = false;
+		entryTransition = false;
+	}
+
+	const activeTransform = $derived(
+		cardEntering
+			? 'scale(0.95) translateY(13px)'
+			: `translateX(${offsetX}px) translateY(${offsetY}px) rotate(${rotation}deg)`
+	);
+
+	const activeTransition = $derived(
+		isDragging
+			? 'none'
+			: (transitioning || entryTransition)
+				? 'transform 0.35s cubic-bezier(0.175, 0.885, 0.32, 1.275)'
+				: 'none'
+	);
+
 	function onPointerDown(e: PointerEvent) {
+		cancelEntryAnimation();
 		if (animating || !currentBook) return;
 		(e.currentTarget as HTMLElement).setPointerCapture(e.pointerId);
 		startX = e.clientX;
@@ -216,6 +252,8 @@
 
 		if (action === 'read_now') {
 			goto(`/books/${book.slug}`);
+		} else {
+			startEntryAnimation();
 		}
 	}
 
@@ -493,8 +531,8 @@
 				bind:this={cardEl}
 				class="absolute inset-0 rounded-2xl overflow-hidden shadow-2xl cursor-grab active:cursor-grabbing z-10"
 				style="
-					transform: translateX({offsetX}px) translateY({offsetY}px) rotate({rotation}deg);
-					transition: {(transitioning && !isDragging) ? 'transform 0.35s cubic-bezier(0.175, 0.885, 0.32, 1.275)' : 'none'};
+					transform: {activeTransform};
+					transition: {activeTransition};
 					touch-action: none;
 				"
 				onpointerdown={onPointerDown}