Jinja2 syntax highlighting + description field + preview toggle

JinjaEditor:
- Custom StreamLanguage parser for Jinja2 syntax highlighting:
  {{ variables }} in blue, {% statements %} in purple, {# comments #} in gray
- Replaced HTML mode (didn't understand Jinja2 syntax)
- Proper monospace font (Consolas/Monaco)

TemplateConfig:
- Added `description` field to model + seed defaults with descriptions
- Description shown on template cards instead of raw template text
- Description input in create/edit form

Preview:
- Toggle behavior: clicking Preview again hides the preview
- Per-slot preview uses preview-raw API (renders current editor content)

i18n: added common.description, templateConfig.descriptionPlaceholder

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/routes/users/+page.svelte

@@ -8,6 +8,7 @@
 	import Loading from '$lib/components/Loading.svelte';
 	import Modal from '$lib/components/Modal.svelte';
 	import ConfirmModal from '$lib/components/ConfirmModal.svelte';
+	import IconButton from '$lib/components/IconButton.svelte';
 
 	const auth = getAuth();
 	let users = $state<any[]>([]);
@@ -101,10 +102,10 @@
 					<p class="font-medium">{user.username}</p>
 					<p class="text-sm text-[var(--color-muted-foreground)]">{user.role} · {t('users.joined')} {new Date(user.created_at).toLocaleDateString()}</p>
 				</div>
-				<div class="flex items-center gap-3">
+				<div class="flex items-center gap-1">
 					{#if user.id !== auth.user?.id}
-						<button onclick={() => openResetPassword(user)} class="text-xs text-[var(--color-muted-foreground)] hover:underline">🔑</button>
-						<button onclick={() => remove(user.id)} class="text-xs text-[var(--color-destructive)] hover:underline">{t('users.delete')}</button>
+						<IconButton icon="mdiKeyVariant" title={t('common.changePassword')} onclick={() => openResetPassword(user)} />
+						<IconButton icon="mdiDelete" title={t('users.delete')} onclick={() => remove(user.id)} variant="danger" />
 					{/if}
 				</div>
 			</div>