feat(sidebar): manage-collective link as last nav entry with spacer

The DesktopSidebar previously had no entry point for /collective/manage,
making member-management and the new common-items / tags subsections
unreachable from the chrome on desktop. The MobileDrawer already linked
it from inside the collective switcher block; desktop didn't.

- Adds a `<div aria-hidden>` divider with `my-2 border-t` to separate
  the section nav (lists / tasks / notes / search) from the manage
  entry.
- Adds a `Users`-iconed link to `/collective/manage` as the last nav
  item, with the same active-state styling as the other entries.
- Not gated by `$enabledSections` (membership management is orthogonal
  to feature toggles — same call as the Admin entry in the footer).
- Reuses the existing `m.manage_title()` Paraglide string; no new
  strings.

Tests: tests/e2e/sidebar-manage-link.test.ts adds SBM-01 (link visible
and navigates) + SBM-02 (divider present in <nav>).

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

apps/web/tests/e2e/sidebar-manage-link.test.ts

@@ -0,0 +1,40 @@
+/**
+ * SBM-series — desktop sidebar manage-collective entry
+ *
+ * The DesktopSidebar gained a last-position link to /collective/manage
+ * after the nav loop, preceded by a visual spacer (divider). The mobile
+ * drawer already had this link; desktop did not, leaving the page
+ * unreachable from the chrome.
+ */
+import { test, expect } from '@playwright/test';
+import { USERS } from '../fixtures/users.js';
+import { loginAs } from '../fixtures/login.js';
+
+const DESKTOP = { width: 1280, height: 800 };
+
+test.describe('Desktop sidebar — manage collective link', () => {
+	test('SBM-01: the manage link is the last nav entry and navigates to /collective/manage', async ({ page }) => {
+		await page.setViewportSize(DESKTOP);
+		await loginAs(page, USERS.ana);
+		await page.goto('/lists');
+
+		const link = page.getByTestId('sidebar-manage-link');
+		await expect(link).toBeVisible({ timeout: 10_000 });
+
+		await link.click();
+		await expect(page).toHaveURL(/\/collective\/manage/);
+	});
+
+	test('SBM-02: a horizontal divider separates the manage link from the section nav', async ({ page }) => {
+		await page.setViewportSize(DESKTOP);
+		await loginAs(page, USERS.ana);
+		await page.goto('/lists');
+
+		// The divider sits inside the same <nav>, immediately before the manage link.
+		const manageLink = page.getByTestId('sidebar-manage-link');
+		await expect(manageLink).toBeVisible({ timeout: 10_000 });
+
+		const dividerCount = await page.locator('nav > div[aria-hidden="true"]').count();
+		expect(dividerCount).toBeGreaterThanOrEqual(1);
+	});
+});