feat: UX improvements — secure webhooks, locale fixes, dynamic languages, UI polish

- Remove top paginator from dashboard events, keep only bottom
- Fix test message locale: pass UI locale to email/matrix bot tests
- Convert webhook auth mode from text input to icon grid selector
- Generate secure UUID tokens for webhook URLs instead of sequential IDs
- Move Recent Payloads into per-provider expandable container (lazy-loaded)
- Make template config languages dynamic via app settings instead of hardcoded
- Change default dev port to 5175

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

@@ -18,6 +18,7 @@
 		external_url: '',
 		telegram_webhook_secret: '',
 		telegram_cache_ttl_hours: '48',
+		supported_locales: 'en,ru',
 	});
 
 	onMount(async () => {
@@ -79,6 +80,21 @@
 			</div>
 		</Card>
 
+		<!-- Locales section -->
+		<Card>
+			<h3 class="text-sm font-semibold mb-4 flex items-center gap-2">
+				<MdiIcon name="mdiTranslate" size={18} />
+				{t('settings.locales')}
+			</h3>
+			<div class="space-y-3">
+				<div>
+					<label class="block text-xs font-medium mb-1">{t('settings.supportedLocales')}<Hint text={t('settings.supportedLocalesHint')} /></label>
+					<input bind:value={settings.supported_locales} placeholder="en,ru,de,fr"
+						class="w-full max-w-md px-3 py-1.5 text-sm border border-[var(--color-border)] rounded-md bg-[var(--color-background)] font-mono" />
+				</div>
+			</div>
+		</Card>
+
 		<Button onclick={save} disabled={saving}>
 			{saving ? t('common.loading') : t('common.save')}
 		</Button>