Adds scheduled events to the feed

Implements NIP-52 scheduled events, allowing users to view and interact with calendar events.

A new `ScheduledEventService` is introduced to manage fetching, storing, and completing scheduled events. A new `ScheduledEventCard` component is introduced for displaying the scheduled events.

src/core/di-container.ts

@@ -136,6 +136,7 @@ export const SERVICE_TOKENS = {
   FEED_SERVICE: Symbol('feedService'),
   PROFILE_SERVICE: Symbol('profileService'),
   REACTION_SERVICE: Symbol('reactionService'),
+  SCHEDULED_EVENT_SERVICE: Symbol('scheduledEventService'),
 
   // Nostr metadata services
   NOSTR_METADATA_SERVICE: Symbol('nostrMetadataService'),