feat(shared-ui,shared-stores): add FavoriteButton component and toggleField utility

FavoriteButton: reusable heart/star/pin toggle with filled/outline states,
accessible labels, configurable colors. toggleField: generic boolean field
toggle for Dexie records (isFavorite, isPinned, etc.) with timestamp.
Includes 11 tests (6 FavoriteButton + 5 toggleField).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-ui/src/molecules/FavoriteButton.svelte

@@ -0,0 +1,64 @@
+<script lang="ts">
+	import { Heart, Star, PushPin } from '@manacore/shared-icons';
+
+	/**
+	 * Reusable favorite/pin toggle button.
+	 * Renders a heart, star, or pin icon that toggles between filled and outline.
+	 */
+
+	interface Props {
+		active: boolean;
+		onclick: () => void;
+		/** Icon variant */
+		variant?: 'heart' | 'star' | 'pin';
+		/** Icon size in pixels */
+		size?: number;
+		/** Active color (CSS color) */
+		activeColor?: string;
+		/** Inactive color (CSS color) */
+		inactiveColor?: string;
+		/** Extra CSS classes on the button */
+		class?: string;
+		/** Accessible label */
+		label?: string;
+	}
+
+	let {
+		active,
+		onclick,
+		variant = 'heart',
+		size = 18,
+		activeColor = variant === 'pin' ? 'var(--color-primary, #3b82f6)' : '#ef4444',
+		inactiveColor = 'currentColor',
+		class: className = '',
+		label,
+	}: Props = $props();
+
+	const defaultLabel = $derived(
+		variant === 'pin'
+			? active
+				? 'Loslösen'
+				: 'Anpinnen'
+			: active
+				? 'Favorit entfernen'
+				: 'Favorit'
+	);
+
+	const icons = { heart: Heart, star: Star, pin: PushPin };
+	const Icon = $derived(icons[variant]);
+</script>
+
+<button
+	type="button"
+	{onclick}
+	class="inline-flex items-center justify-center rounded-md p-1 transition-colors hover:bg-black/5 dark:hover:bg-white/10 {className}"
+	aria-label={label ?? defaultLabel}
+	title={label ?? defaultLabel}
+>
+	<Icon
+		{size}
+		weight={active ? 'fill' : 'regular'}
+		class="transition-colors"
+		style="color: {active ? activeColor : inactiveColor}"
+	/>
+</button>