Add delete task functionality for task authors

Added ability for task authors to delete their own tasks from the expanded
view in the task feed.

**Features:**
- Delete button visible only to task author in expanded task view
- Confirmation dialog with destructive styling
- Publishes NIP-09 deletion event (kind 5) with 'a' tag referencing the
  task's event address (kind:pubkey:d-tag format)
- Real-time deletion handling via FeedService routing
- Optimistic local state update for immediate UI feedback

**Implementation:**
- Added deleteTask() method to ScheduledEventService
- Added handleTaskDeletion() for processing incoming deletion events
- Updated FeedService to route kind 31922 deletions to ScheduledEventService
- Added delete button and dialog flow to ScheduledEventCard component
- Integrated with existing confirmation dialog pattern

**Permissions:**
- Only task authors can delete tasks (enforced by isAuthor check)
- NIP-09 validation: relays only accept deletion from event author
- Pubkey verification in handleTaskDeletion()

**Testing:**
- Created tasks and verified delete button appears for author only
- Confirmed deletion removes task from UI immediately
- Verified deletion persists after refresh
- Tested with multiple users - others cannot delete

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/modules/nostr-feed/components/NostrFeed.vue

@@ -107,6 +107,7 @@ const {
   startTask,
   completeEvent,
   unclaimTask,
+  deleteTask,
   allCompletions
 } = useScheduledEvents()
 
@@ -301,6 +302,15 @@ async function onUnclaimTask(event: ScheduledEvent, occurrence?: string) {
   }
 }
 
+async function onDeleteTask(event: ScheduledEvent) {
+  console.log('🗑️ NostrFeed: Deleting task:', event.title)
+  try {
+    await deleteTask(event)
+  } catch (error) {
+    console.error('❌ Failed to delete task:', error)
+  }
+}
+
 // Handle collapse toggle with cascading behavior
 function onToggleCollapse(postId: string) {
   const newCollapsed = new Set(collapsedPosts.value)
@@ -555,6 +565,7 @@ function cancelDelete() {
               @start-task="onStartTask"
               @complete-task="onCompleteTask"
               @unclaim-task="onUnclaimTask"
+              @delete-task="onDeleteTask"
             />
           </div>
           <div v-else class="text-center py-3 text-muted-foreground text-sm px-4">