feat: Centralize configuration management for Nostr and API settings

- Introduce a new config module to manage Nostr relays, admin pubkeys, and API settings.
- Update components to utilize the centralized config instead of environment variables directly.
- Refactor relevant files to improve maintainability and reduce reliance on environment variables.

src/lib/api/events.ts

@@ -1,7 +1,8 @@
 import type { Event, EventsApiError } from '../types/event'
+import { config } from '@/lib/config'
 
-const API_BASE_URL = import.meta.env.VITE_API_BASE_URL || 'http://lnbits'
-const API_KEY = import.meta.env.VITE_API_KEY
+const API_BASE_URL = config.api.baseUrl || 'http://lnbits'
+const API_KEY = config.api.key
 
 export async function fetchEvents(allWallets = true): Promise<Event[]> {
   try {