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/lib/stores/caches.svelte.ts

@@ -74,6 +74,23 @@ export const capabilitiesCache = (() => {
 	};
 })();
 
+/** Supported template locales — fetched from app settings. */
+export const supportedLocalesCache = (() => {
+	let data = $state<string[]>(['en', 'ru']);
+	let fetchedAt = $state(0);
+	const TTL = 300_000; // 5 minutes
+	return {
+		get items() { return data; },
+		async fetch(force = false): Promise<string[]> {
+			if (!force && fetchedAt > 0 && Date.now() - fetchedAt < TTL) return data;
+			const { api } = await import('$lib/api');
+			data = await api('/settings/locales');
+			fetchedAt = Date.now();
+			return data;
+		},
+	};
+})();
+
 /**
  * All caches keyed by entity type — for search palette and crosslink resolution.
  */