Uses array for completions to improve reactivity

Changes the `allCompletions` computed property to return an array instead of a Map.
This improves reactivity in the component that uses it, as Vue can more efficiently track changes in an array.
Also simplifies the pubkey extraction process.

src/modules/nostr-feed/composables/useScheduledEvents.ts

@@ -125,10 +125,11 @@ export function useScheduledEvents() {
   })
 
   /**
-   * Get all completions (reactive)
+   * Get all completions (reactive) - returns array for better reactivity
    */
   const allCompletions = computed(() => {
-    return scheduledEventService?.completions ?? new Map()
+    if (!scheduledEventService?.completions) return []
+    return Array.from(scheduledEventService.completions.values())
   })
 
   return {