feat: locale-aware notification templates + UX improvements

- Add locale support to notification templates (matching command template
  pattern): TemplateSlot now has locale field with (config_id, slot_name,
  locale) uniqueness, nested API format {slot: {locale: template}}
- Migration merges separate EN/RU system configs into unified per-provider
  configs; seeds create one config per provider with multi-locale slots
- Locale-aware dispatch with EN fallback in NotificationDispatcher
- Frontend locale tabs (EN/RU) on template config editor
- Fix tracking config cards not showing default provider icons
- Global provider filter, search palette, and various UX polish

frontend/src/lib/grid-items.ts

@@ -6,6 +6,21 @@
 import { t } from '$lib/i18n';
 import type { GridItem } from '$lib/components/IconGridSelect.svelte';
 
+/** Default icon for each provider type. Use instead of hardcoded 'mdiServer'. */
+const PROVIDER_TYPE_ICONS: Record<string, string> = {
+	immich: 'mdiImageMultiple',
+	gitea: 'mdiGit',
+	planka: 'mdiViewDashboard',
+	scheduler: 'mdiClockOutline',
+};
+
+/** Get the default icon for a provider, falling back by type then generic. */
+export function providerDefaultIcon(provider: { icon?: string; type?: string }): string {
+	if (provider.icon) return provider.icon;
+	if (provider.type && PROVIDER_TYPE_ICONS[provider.type]) return PROVIDER_TYPE_ICONS[provider.type];
+	return 'mdiServer';
+}
+
 // --- Sort ---
 
 export const sortByItems = (): GridItem[] => [
@@ -108,8 +123,8 @@ export const providerTypeFilterItems = (): GridItem[] => [
 // --- Provider type ---
 
 export const providerTypeItems = (): GridItem[] => [
-	{ value: 'immich', icon: 'mdiCamera', label: t('providers.typeImmich'), desc: t('gridDesc.providerImmich') },
-	{ value: 'gitea', icon: 'mdiGit', label: t('providers.typeGitea'), desc: t('gridDesc.providerGitea') },
-	{ value: 'planka', icon: 'mdiViewDashboard', label: t('providers.typePlanka'), desc: t('gridDesc.providerPlanka') },
-	{ value: 'scheduler', icon: 'mdiClockOutline', label: t('providers.typeScheduler'), desc: t('gridDesc.providerScheduler') },
+	{ value: 'immich', icon: PROVIDER_TYPE_ICONS.immich, label: t('providers.typeImmich'), desc: t('gridDesc.providerImmich') },
+	{ value: 'gitea', icon: PROVIDER_TYPE_ICONS.gitea, label: t('providers.typeGitea'), desc: t('gridDesc.providerGitea') },
+	{ value: 'planka', icon: PROVIDER_TYPE_ICONS.planka, label: t('providers.typePlanka'), desc: t('gridDesc.providerPlanka') },
+	{ value: 'scheduler', icon: PROVIDER_TYPE_ICONS.scheduler, label: t('providers.typeScheduler'), desc: t('gridDesc.providerScheduler') },
 ];