fix(admin): address PR review feedback from all personas

Blockers resolved:
- localStorage key collision: UsersListPanel/GroupsListPanel/TagsListPanel
  now each use their own key (admin_*_list_collapsed)
- $effect autocollapse replaced with $derived(autocollapse || manualCollapse)
  across all three list panels (Felix — Svelte 5 rule violation)
- groups/new: add READ_ALL and ANNOTATE_ALL to available standard permissions
- Mobile back-to-list links added to all five detail panel headers (md:hidden)
  so users landing directly on a detail URL on mobile can navigate back
- onDestroy(() => stopPolling()) added to system/+page.svelte (Tobias)

High priority resolved:
- Permission labels in groups/[id] and groups/new now use Paraglide i18n keys
  (admin_perm_read_all, admin_perm_annotate_all, etc.) across de/en/es
- $derived used for permission arrays (reactive i18n) — Felix Svelte 5 rule
- UserGroup type in +layout.server.ts now uses generated API type (Markus/Felix)
- discardTarget annotation changed to variable-level type annotation

Accessibility (Leonie):
- EntityNav tablet icon strip buttons: min-h-[44px] for WCAG 2.5.8 compliance
- Flyout focus management: openFlyout() focuses first link, closeFlyout()
  returns focus to the trigger button that opened it
- Flyout animation replaced: broken inline style -> transition:fly={{ x: -160 }}

Tests (Sara/Felix):
- localStorage key assertion tests added per panel
- localStorage.removeItem calls updated to use the panel-specific keys
- page.server.spec.ts added for groups/[id] and tags/[id] delete actions
- Polling lifecycle tests added to system/page.svelte.spec.ts

Note: Paraglide types for new admin_perm_* keys regenerate automatically on
next npm run dev (Vite plugin). No manual compilation step needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/admin/system/+page.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+import { onDestroy } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
 
 let backfillResult: number | null = $state(null);
@@ -52,9 +53,10 @@ async function triggerImport() {
 
 $effect(() => {
 	fetchImportStatus();
-	return () => stopPolling();
 });
 
+onDestroy(() => stopPolling());
+
 async function backfillVersions() {
 	backfillLoading = true;
 	backfillResult = null;

frontend/src/routes/admin/system/page.svelte.spec.ts

@@ -1,4 +1,4 @@
-import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi, type MockInstance } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page } from 'vitest/browser';
 import Page from './+page.svelte';
@@ -134,3 +134,56 @@ describe('Admin system page — mass import card', () => {
 		await expect.element(page.getByRole('button', { name: /Erneut starten/i })).toBeInTheDocument();
 	});
 });
+
+// ─── Polling lifecycle ────────────────────────────────────────────────────────
+
+describe('Admin system page — polling lifecycle', () => {
+	let setIntervalSpy: MockInstance;
+	let clearIntervalSpy: MockInstance;
+
+	beforeEach(() => {
+		setIntervalSpy = vi.spyOn(globalThis, 'setInterval');
+		clearIntervalSpy = vi.spyOn(globalThis, 'clearInterval');
+	});
+
+	afterEach(() => {
+		setIntervalSpy.mockRestore();
+		clearIntervalSpy.mockRestore();
+	});
+
+	it('starts polling when initial status is RUNNING', async () => {
+		vi.stubGlobal(
+			'fetch',
+			vi.fn().mockResolvedValue({
+				ok: true,
+				json: async () => ({
+					state: 'RUNNING',
+					message: 'Import läuft...',
+					processed: 0,
+					startedAt: '2026-01-01T10:00:00'
+				})
+			})
+		);
+		render(Page, {});
+		await expect.element(page.getByText(/Import läuft/i)).toBeInTheDocument();
+		expect(setIntervalSpy).toHaveBeenCalled();
+	});
+
+	it('does not start polling when initial status is IDLE', async () => {
+		vi.stubGlobal(
+			'fetch',
+			vi.fn().mockResolvedValue({
+				ok: true,
+				json: async () => ({
+					state: 'IDLE',
+					message: '',
+					processed: 0,
+					startedAt: null
+				})
+			})
+		);
+		render(Page, {});
+		await expect.element(page.getByRole('button', { name: /Import starten/i })).toBeInTheDocument();
+		expect(setIntervalSpy).not.toHaveBeenCalled();
+	});
+});