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-stores/src/toggle-field.ts

@@ -0,0 +1,42 @@
+/**
+ * Generic boolean field toggle for Dexie tables.
+ *
+ * Standardizes the common pattern of toggling a boolean field (isFavorite, isPinned, etc.)
+ * on a record in IndexedDB. Reads current value, flips it, updates with timestamp.
+ *
+ * @example
+ * ```typescript
+ * import { toggleField } from '@manacore/shared-stores';
+ * import { db } from '$lib/data/database';
+ *
+ * // In your store:
+ * async function toggleFavorite(id: string) {
+ *   return toggleField(db.table('contacts'), id, 'isFavorite');
+ * }
+ * ```
+ */
+
+import type { Table } from 'dexie';
+
+/**
+ * Toggle a boolean field on a Dexie record.
+ * @returns The new value of the field after toggling.
+ */
+export async function toggleField<T>(
+	table: Table<T, string>,
+	id: string,
+	field: string
+): Promise<boolean> {
+	const record = await table.get(id);
+	if (!record) throw new Error(`Record ${id} not found`);
+
+	const current = !!(record as Record<string, unknown>)[field];
+	const newValue = !current;
+
+	await table.update(id, {
+		[field]: newValue,
+		updatedAt: new Date().toISOString(),
+	} as Partial<T>);
+
+	return newValue;
+}