fix(highlights): improve relay indicator tooltip accuracy

Update tooltip text to be more accurate about relay information:
- Show 'Published to X relays' for user-created highlights with publishedRelays
- Show 'Seen on X relays' for highlights with seenOnRelays tracking
- Show 'Fetched from network' for highlights without relay metadata
- Add seenOnRelays field to Highlight type for future relay tracking

src/types/highlights.ts

@@ -16,7 +16,8 @@ export interface Highlight {
   // Level classification (computed based on user's context)
   level?: HighlightLevel
   // Relay tracking for offline/local-only highlights
-  publishedRelays?: string[] // URLs of relays that acknowledged this event
+  publishedRelays?: string[] // URLs of relays where this was published (for user-created highlights)
+  seenOnRelays?: string[] // URLs of relays where this event was fetched from
   isLocalOnly?: boolean // true if only published to local relays
   isOfflineCreated?: boolean // true if created while in flight mode (offline)
   isSyncing?: boolean // true if currently being synced to remote relays