perf(pokedex): send the box grid as packed rows with the page

The server load fetched a full combined-data page at a 9999 item page size,
carrying detail text and ownership fields the grid never renders, and the client
re-fetched the same payload after hydration.

Load a trimmed grid row instead and pack it as positional tuples so field names
are not repeated for every one of a thousand-plus entries. Entry detail is
fetched on demand from the new per-entry endpoint when a cell is opened, and the
grid marks itself interactive so other page-start work can queue behind it.

tests/unit/criticalPageWork.test.ts

@@ -0,0 +1,103 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { afterCriticalPageWork, markGridInteractive } from '$lib/utils/criticalPageWork';
+
+describe('optional work scheduling', () => {
+	let events: EventTarget & Record<string, unknown>;
+	let idle: (() => void) | undefined;
+	beforeEach(() => {
+		vi.useFakeTimers();
+		events = Object.assign(new EventTarget(), {
+			setTimeout,
+			clearTimeout,
+			requestIdleCallback: vi.fn((callback: () => void) => {
+				idle = callback;
+				return 1;
+			}),
+			cancelIdleCallback: vi.fn()
+		});
+		idle = undefined;
+		vi.stubGlobal('window', events);
+		vi.stubGlobal('location', { pathname: '/pokedex/example' });
+		vi.stubGlobal('document', { querySelector: () => null });
+		vi.stubGlobal('requestAnimationFrame', (callback: () => void) => setTimeout(callback, 16));
+		vi.stubGlobal('cancelAnimationFrame', clearTimeout);
+	});
+	afterEach(() => {
+		vi.useRealTimers();
+		vi.unstubAllGlobals();
+	});
+
+	it('waits for interactive cells, coalesces events, then runs at idle once', () => {
+		const run = vi.fn();
+		afterCriticalPageWork(run);
+		vi.advanceTimersByTime(1000);
+		expect(run).not.toHaveBeenCalled();
+		events.dispatchEvent(new Event('livingdex:grid-interactive'));
+		events.dispatchEvent(new Event('livingdex:grid-interactive'));
+		vi.advanceTimersByTime(16);
+		expect(events.requestIdleCallback).toHaveBeenCalledTimes(1);
+		expect(run).not.toHaveBeenCalled();
+		idle!();
+		vi.advanceTimersByTime(5000);
+		expect(run).toHaveBeenCalledTimes(1);
+	});
+	it('falls back after five seconds if no grid becomes interactive', () => {
+		const run = vi.fn();
+		afterCriticalPageWork(run);
+		vi.advanceTimersByTime(4999);
+		expect(run).not.toHaveBeenCalled();
+		vi.advanceTimersByTime(1);
+		expect(run).toHaveBeenCalledTimes(1);
+	});
+	it('cancels work after navigation or an explicit refresh takes over', () => {
+		const run = vi.fn();
+		const cancel = afterCriticalPageWork(run);
+		events.dispatchEvent(new Event('livingdex:grid-interactive'));
+		vi.advanceTimersByTime(16);
+		cancel();
+		idle!();
+		vi.advanceTimersByTime(5000);
+		expect(run).not.toHaveBeenCalled();
+	});
+	it('does not announce a grid with no populated cells', () => {
+		const listener = vi.fn();
+		events.addEventListener('livingdex:grid-interactive', listener);
+		markGridInteractive();
+		expect(listener).not.toHaveBeenCalled();
+	});
+	it('schedules other pages without waiting for a grid, even without idle callbacks', () => {
+		vi.stubGlobal('location', { pathname: '/backup-settings' });
+		delete events.requestIdleCallback;
+		const run = vi.fn();
+		afterCriticalPageWork(run);
+		vi.advanceTimersByTime(32);
+		expect(run).toHaveBeenCalledTimes(1);
+	});
+	it('marks populated cells once and allows work registered after hydration', () => {
+		let ready = false;
+		const grid = {
+			setAttribute: () => {
+				ready = true;
+			}
+		};
+		const cell = { closest: () => grid };
+		vi.stubGlobal('document', {
+			querySelector: (selector: string) =>
+				selector === '[data-entry-index]' ? cell : ready ? grid : null
+		});
+		const mark = vi.fn();
+		vi.stubGlobal('performance', { mark });
+		markGridInteractive();
+		markGridInteractive();
+		expect(mark).toHaveBeenCalledTimes(1);
+		const run = vi.fn();
+		afterCriticalPageWork(run);
+		vi.advanceTimersByTime(16);
+		idle!();
+		expect(run).toHaveBeenCalledTimes(1);
+	});
+	it('does not access the DOM during SSR', () => {
+		vi.stubGlobal('window', undefined);
+		expect(() => markGridInteractive()).not.toThrow();
+	});
+});