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/bots/MatrixBotTab.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 	import { api } from '$lib/api';
-	import { t } from '$lib/i18n';
+	import { t, getLocale } from '$lib/i18n';
 	import { matrixBotsCache } from '$lib/stores/caches.svelte';
 	import PageHeader from '$lib/components/PageHeader.svelte';
 	import Card from '$lib/components/Card.svelte';
@@ -70,7 +70,7 @@
 	async function testMatrixBot(botId: number) {
 		matrixTesting = { ...matrixTesting, [botId]: true };
 		try {
-			const res = await api(`/matrix-bots/${botId}/test`, { method: 'POST' });
+			const res = await api(`/matrix-bots/${botId}/test?locale=${getLocale()}`, { method: 'POST' });
 			if (res.success) snackSuccess(t('snack.matrixBotTestOk'));
 			else snackError(res.error || t('matrixBot.operationFailed'));
 		} catch (err: any) { snackError(err.message); }