fix: align WakeUp handling with spec semantics (p-tags = authors)

A previous commit misread the spec: p-tags on a WakeUp identify the
AUTHORS of the referenced events (the people whose events are the
subject of the wake-up), not the recipients. The consumer's existing
npub-in-p-tag match is therefore correct — "is this logged-in account
the author of a referenced event?".

- Revert WakeUpEvent.build() back to notify(about.toPTag()) and replace
  the comment with a spec-accurate one.
- In wakeUpFor, source author pubkeys from event.authorKeys() (p-tags,
  canonical) first, merge in the e-tag author hints, and fall back to
  the WakeUp signer only when both are empty. Bound by MAX_WAKEUP_REFS.

computeReplyTo and the referenced-event fetch path remain untouched —
those fixes are orthogonal to the p-tag semantic.

amethyst/src/main/java/com/vitorpamplona/amethyst/service/notifications/EventNotificationConsumer.kt

@@ -204,16 +204,17 @@ class EventNotificationConsumer(
             return
         }
 
-        // The referenced event's author is who the user will see in the final
-        // notification ("Alice zapped you"). The WakeUp's own pubKey is typically
-        // a push bot and not useful. Fall back to it only when the `e` tag omits
-        // the author hint.
+        // Per spec, p-tags on a WakeUp are the authors of the referenced
+        // events; those are whose metadata we need to render the notification.
+        // Fall back to e-tag author hints and finally to the WakeUp signer.
         val referencedNotes = referencedTags.map { LocalCache.getOrCreateNote(it.eventId) }
-        val authorCandidates =
-            referencedTags
-                .mapNotNull { it.author }
+        val authorKeys =
+            (event.authorKeys() + referencedTags.mapNotNull { it.author })
                 .distinct()
                 .ifEmpty { listOf(event.pubKey) }
+        val authorCandidates =
+            authorKeys
+                .take(MAX_WAKEUP_REFS)
                 .map { LocalCache.getOrCreateUser(it) }
 
         coroutineScope {