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/users/new/+page.svelte

@@ -10,7 +10,7 @@ let { data, form } = $props();
 
 let isDirty = $state(false);
 let showUnsavedWarning = $state(false);
-let discardTarget = $state<string | null>(null);
+let discardTarget: string | null = $state(null);
 
 beforeNavigate(({ cancel, to }) => {
 	if (isDirty) {
@@ -24,6 +24,21 @@ beforeNavigate(({ cancel, to }) => {
 <div class="flex flex-1 flex-col overflow-hidden">
 	<!-- Detail panel header -->
 	<div class="flex items-center border-b border-line px-5 py-3">
+		<a
+			href="/admin/users"
+			class="mr-3 inline-flex items-center gap-1 text-xs text-ink-3 hover:text-ink md:hidden"
+		>
+			<svg
+				class="h-4 w-4"
+				fill="none"
+				viewBox="0 0 24 24"
+				stroke="currentColor"
+				stroke-width="2"
+				aria-hidden="true"
+			>
+				<path stroke-linecap="round" stroke-linejoin="round" d="M15 19l-7-7 7-7" />
+			</svg>
+		</a>
 		<h2 class="flex-1 font-sans text-sm font-bold text-ink">{m.admin_user_new_heading()}</h2>
 	</div>