feat(admin/groups): add groups entity with master-detail sub-routes

Creates the full groups section under /admin/groups/:
- +layout.server.ts: loads groups list via GET /api/groups
- GroupsListPanel.svelte: left list panel (name + permission count, active state)
- +layout.svelte: composes list panel + children slot
- +page.svelte: empty selection prompt
- [id]/+page.server.ts: update (PATCH) and delete actions
- [id]/+page.svelte: edit detail panel with Standard/Administrative permission sections
- new/+page.svelte and +page.server.ts: create group form

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

frontend/src/routes/admin/groups/new/+page.svelte

@@ -0,0 +1,117 @@
+<script lang="ts">
+import { enhance } from '$app/forms';
+import { m } from '$lib/paraglide/messages.js';
+
+const availableStandard = [{ value: 'WRITE_ALL', label: 'Lesen & Schreiben' }];
+const availableAdmin = [
+	{ value: 'ADMIN', label: 'Vollzugriff (Admin)' },
+	{ value: 'ADMIN_USER', label: 'Benutzer verwalten' },
+	{ value: 'ADMIN_TAG', label: 'Schlagworte verwalten' },
+	{ value: 'ADMIN_PERMISSION', label: 'Berechtigungen verwalten' }
+];
+
+let { form } = $props();
+</script>
+
+<div class="flex flex-1 flex-col overflow-hidden">
+	<!-- Detail panel header -->
+	<div
+		class="flex items-center border-b border-green-200 bg-green-50 px-5 py-3 dark:border-green-900 dark:bg-green-950/30"
+	>
+		<h2 class="flex-1 font-sans text-sm font-bold text-green-800 dark:text-green-300">
+			{m.admin_group_new_heading()}
+		</h2>
+	</div>
+
+	<!-- Scrollable body -->
+	<div class="flex-1 overflow-y-auto px-5 py-5">
+		{#if form?.error}
+			<div class="mb-5 rounded border border-red-200 bg-red-50 p-3 text-sm text-red-700">
+				{form.error}
+			</div>
+		{/if}
+
+		<form id="new-group-form" method="POST" use:enhance class="space-y-5">
+			<!-- Name card -->
+			<div class="rounded-sm border border-line bg-surface p-5 shadow-sm">
+				<h3 class="mb-3 text-xs font-bold tracking-widest text-ink-3 uppercase">
+					{m.admin_col_name()}
+				</h3>
+				<input
+					type="text"
+					name="name"
+					placeholder={m.admin_group_name_placeholder()}
+					required
+					class="w-full rounded-sm border border-line bg-surface px-3 py-2 text-sm text-ink placeholder:text-ink-3 focus:ring-1 focus:ring-primary focus:outline-none"
+				/>
+			</div>
+
+			<!-- Standard permissions -->
+			<div class="rounded-sm border border-line bg-surface p-5 shadow-sm">
+				<h3 class="mb-3 text-xs font-bold tracking-widest text-ink-3 uppercase">
+					{m.admin_groups_section_standard()}
+				</h3>
+				<div class="space-y-2">
+					{#each availableStandard as perm (perm.value)}
+						<label class="flex items-center gap-2 text-sm text-ink">
+							<input
+								type="checkbox"
+								name="permissions"
+								value={perm.value}
+								class="rounded border-line text-primary focus:ring-primary"
+							/>
+							<span class="font-mono text-xs font-bold uppercase">{perm.value}</span>
+							<span class="text-ink-3">— {perm.label}</span>
+						</label>
+					{/each}
+				</div>
+			</div>
+
+			<!-- Administrative permissions -->
+			<div
+				class="rounded-sm border border-amber-200 bg-amber-50 p-5 shadow-sm dark:border-amber-900 dark:bg-amber-950/30"
+			>
+				<h3
+					class="mb-3 text-xs font-bold tracking-widest text-amber-700 uppercase dark:text-amber-400"
+				>
+					{m.admin_groups_section_administrative()}
+				</h3>
+				<div class="space-y-2">
+					{#each availableAdmin as perm (perm.value)}
+						<label
+							class="flex items-center gap-2 text-sm {perm.value === 'ADMIN'
+								? 'font-bold text-red-700 dark:text-red-400'
+								: 'text-ink'}"
+						>
+							<input
+								type="checkbox"
+								name="permissions"
+								value={perm.value}
+								class="rounded border-line text-primary focus:ring-primary"
+							/>
+							<span class="font-mono text-xs font-bold uppercase">{perm.value}</span>
+							<span class="font-normal text-ink-3">— {perm.label}</span>
+						</label>
+					{/each}
+				</div>
+			</div>
+		</form>
+	</div>
+
+	<!-- Docked footer -->
+	<div class="flex items-center justify-between border-t border-line bg-surface px-5 py-3">
+		<a
+			href="/admin/groups"
+			class="font-sans text-xs font-bold tracking-widest text-ink-2 uppercase hover:text-ink"
+		>
+			{m.btn_cancel()}
+		</a>
+		<button
+			type="submit"
+			form="new-group-form"
+			class="rounded-sm bg-primary px-5 py-2 font-sans text-xs font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-80"
+		>
+			{m.btn_create()}
+		</button>
+	</div>
+</div>