feat(documents): paginate search with a Pagination control

Frontend side of the /documents pagination work. The page.server.ts load
reads ?page= from the URL, forwards page+size=50 to the backend, and
exposes the new totalElements/pageNumber/pageSize/totalPages fields on
`data`. +page.svelte renders a <Pagination> component below the result
list; buildPageHref preserves every filter param and only updates page.
The existing triggerSearch debounce flow intentionally drops `page`
when any filter changes, so filter edits reset to page 0 automatically.

<Pagination> uses plain <a href> links (not goto) so SvelteKit's default
scroll restoration scrolls new pages to the top — the expected senior-UX
behaviour. Decorative chevrons wrapped in aria-hidden spans, 44px touch
targets, focus-visible ring, stacks vertically under 640px. The control
hides itself when totalPages ≤ 1.

Test coverage: 9 cases on Pagination (label, aria-current, prev/next
enable/disable, makeHref invocation, decorative chevron, touch target),
plus a filter-reset assertion on +page.svelte (page 5 → edit q →
goto URL must drop page=). Adds i18n keys in de/en/es. Manual edit to
api.ts pending a post-merge npm run generate:api against a rebuilt
dev backend. (#315)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/routes/documents/page.svelte.spec.ts

@@ -118,4 +118,20 @@ describe('documents page — URL building', () => {
 			expect.objectContaining({ keepFocus: true, noScroll: true })
 		);
 	});
+
+	it('filter change does not carry the current page — goto URL drops page param', async () => {
+		const { goto } = await import('$app/navigation');
+		vi.mocked(goto).mockClear();
+
+		// User is mid-way through results at page 5; change the search text.
+		render(Page, { data: makeData({ q: 'old', pageNumber: 5 }) });
+
+		const input = page.getByRole('textbox', { name: SEARCH_LABEL });
+		await input.fill('Brief');
+		vi.advanceTimersByTime(500);
+
+		const [url] = vi.mocked(goto).mock.calls[0];
+		expect(url).toContain('q=Brief');
+		expect(url).not.toContain('page=');
+	});
 });