feat: comprehensive code review fixes + receivers-only architecture

Security:
- Refuse startup with default secret_key in production (was just logging)
- Settings endpoint now requires admin role
- Password validation on initial setup
- DOM-based HTML sanitizer replaces regex in template previews
- Add *.log to .gitignore

Performance & reliability:
- Token refresh deduplication prevents race condition on concurrent 401s
- Theme media query listener registered once (no leak)
- IconPicker uses $derived instead of function call per render
- Snackbar uses single-batch state update instead of while loop
- Replace 11 inline hover handlers with CSS :hover in layout

Architecture - receivers-only:
- Delivery endpoints (chat_id, email, url, room_id, topic) now stored
  exclusively in TargetReceiver rows, never in target.config
- Migration extracts existing delivery fields to receiver rows
- Notifier and dispatcher remove all config fallbacks
- Frontend targets page shows receivers list per target with
  add/remove/toggle/test per receiver
- Single-receiver test endpoint: POST /targets/{id}/receivers/{id}/test

Code quality:
- Extract AuthLayout.svelte from login/setup (150 lines CSS dedup)
- Split telegram-bots page (754→51 lines + 3 tab components)
- Split notification-trackers page (547→432 lines + 4 components)
- Deduplicate _send_reply into shared handler.send_reply()
- Add locale column to template models, replace name-based detection
- Fix delete_notification_tracker dead protection check
- Fix check_telegram_bot query (filter by type, remove bogus OR)
- Add graceful scheduler shutdown in lifespan
- Consistent /bots?tab=telegram URLs across all nav links

i18n:
- Error page, chat actions, target types, provider types internationalized
- All new receiver UI strings in EN + RU

frontend/src/lib/api.ts

@@ -0,0 +1,98 @@
+/**
+ * API client with JWT auth for the Notify Bridge backend.
+ */
+
+const API_BASE = '/api';
+
+function getToken(): string | null {
+	if (typeof window === 'undefined') return null;
+	return localStorage.getItem('access_token');
+}
+
+export function setTokens(access: string, refresh: string) {
+	localStorage.setItem('access_token', access);
+	localStorage.setItem('refresh_token', refresh);
+}
+
+export function clearTokens() {
+	localStorage.removeItem('access_token');
+	localStorage.removeItem('refresh_token');
+}
+
+export function isAuthenticated(): boolean {
+	return !!getToken();
+}
+
+let refreshPromise: Promise<boolean> | null = null;
+
+async function refreshAccessToken(): Promise<boolean> {
+	if (refreshPromise) return refreshPromise;
+	refreshPromise = doRefreshAccessToken().finally(() => {
+		refreshPromise = null;
+	});
+	return refreshPromise;
+}
+
+async function doRefreshAccessToken(): Promise<boolean> {
+	if (typeof window === 'undefined') return false;
+	const refreshToken = localStorage.getItem('refresh_token');
+	if (!refreshToken) return false;
+
+	try {
+		const res = await fetch(`${API_BASE}/auth/refresh`, {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({ refresh_token: refreshToken })
+		});
+		if (res.ok) {
+			const data = await res.json();
+			setTokens(data.access_token, data.refresh_token);
+			return true;
+		}
+	} catch {
+		// ignore
+	}
+	return false;
+}
+
+export async function api<T = any>(
+	path: string,
+	options: RequestInit = {}
+): Promise<T> {
+	const token = getToken();
+	const headers: Record<string, string> = {
+		'Content-Type': 'application/json',
+		...(options.headers as Record<string, string>)
+	};
+	if (token) {
+		headers['Authorization'] = `Bearer ${token}`;
+	}
+
+	let res = await fetch(`${API_BASE}${path}`, { ...options, headers });
+
+	// Try token refresh on 401
+	if (res.status === 401 && token) {
+		const refreshed = await refreshAccessToken();
+		if (refreshed) {
+			headers['Authorization'] = `Bearer ${getToken()}`;
+			res = await fetch(`${API_BASE}${path}`, { ...options, headers });
+		}
+	}
+
+	if (res.status === 401) {
+		clearTokens();
+		if (typeof window !== 'undefined') {
+			window.location.href = '/login';
+		}
+		throw new Error('Unauthorized');
+	}
+
+	if (res.status === 204) return undefined as T;
+
+	if (!res.ok) {
+		const err = await res.json().catch(() => ({ detail: res.statusText }));
+		throw new Error(err.detail || `HTTP ${res.status}`);
+	}
+
+	return res.json();
+}