feat(offline): open entry details from the saved snapshot

Opening an entry while offline needed a request that could not be made. Read it
from the snapshot claimed by the signed-in account instead, re-checking
ownership after the read so a sign-in mid-read cannot surface another account's
data, and let controls marked data-offline-action stay usable in read-only mode.

tests/unit/offlineEntry.test.ts

@@ -0,0 +1,58 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+vi.mock('$env/static/public', () => ({ PUBLIC_USE_LOCAL_POKEMON_SPRITE_FOLDER: 'true' }));
+import { readOfflineEntry } from '$lib/stores/offlineSync';
+
+describe('offline detail snapshots', () => {
+	const row = {
+		pokedexEntry: { _id: '1', catchInformation: 'Full instructions' },
+		catchRecord: { personalNotes: 'Saved note' }
+	};
+	function snapshot(owner = 'owner', ageMs = 0, includeEntry = true) {
+		const meta = {
+			userId: owner,
+			format: 2,
+			dataCache: `livingdex-offline-data-v1-${owner}-copy`,
+			generatedAt: new Date(Date.now() - ageMs).toISOString()
+		};
+		const cache = {
+			keys: async () => ['livingdex-offline-meta-v1', meta.dataCache],
+			open: async (name: string) => ({
+				match: async () =>
+					new Response(
+						JSON.stringify(
+							name === 'livingdex-offline-meta-v1'
+								? meta
+								: {
+										userId: owner,
+										version: 1,
+										pokedexes: [{ pokedex: { _id: 'dex' }, entries: includeEntry ? [row] : [] }]
+									}
+						)
+					)
+			})
+		};
+		vi.stubGlobal('window', { caches: cache });
+		vi.stubGlobal('caches', cache);
+	}
+	afterEach(() => vi.unstubAllGlobals());
+	it.each([0, 60 * 60 * 1000])(
+		'uses a matching full snapshot offline even when %i ms old',
+		async (age) => {
+			snapshot('owner', age);
+			expect(await readOfflineEntry('owner', 'dex', '1')).toEqual(row);
+		}
+	);
+	it('never reads another account snapshot', async () => {
+		snapshot('other');
+		expect(await readOfflineEntry('owner', 'dex', '1')).toBeNull();
+	});
+	it('reports missing entries and dexes without fabricating details', async () => {
+		snapshot('owner', 0, false);
+		expect(await readOfflineEntry('owner', 'dex', '1')).toBeNull();
+		expect(await readOfflineEntry('owner', 'missing', '1')).toBeNull();
+	});
+	it('works without Cache Storage', async () => {
+		vi.stubGlobal('window', {});
+		expect(await readOfflineEntry('owner', 'dex', '1')).toBeNull();
+	});
+});