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.

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/experimental/notifications/wake/WakeUpEvent.kt

@@ -35,7 +35,7 @@ import com.vitorpamplona.quartz.nip01Core.tags.kinds.kind
 import com.vitorpamplona.quartz.nip01Core.tags.people.PTag
 import com.vitorpamplona.quartz.nip01Core.tags.people.PTag.Companion.parse
 import com.vitorpamplona.quartz.nip01Core.tags.people.PTag.Companion.parseKey
-import com.vitorpamplona.quartz.nip01Core.tags.people.taggedUsers
+import com.vitorpamplona.quartz.nip01Core.tags.people.toPTag
 import com.vitorpamplona.quartz.nip31Alts.alt
 import com.vitorpamplona.quartz.utils.TimeUtils
 import kotlinx.serialization.json.JsonNull.content
@@ -68,10 +68,10 @@ class WakeUpEvent(
         const val KIND = 23903
         const val ALT_DESCRIPTION = "WakeUp"
 
-        // Tags the audience of [about] (its `p` tags) as the recipients to wake up.
-        // The about event's author is NOT tagged: a WakeUp about a zap from Alice
-        // to Bob should notify Bob, not Alice. Callers can add more recipients via
-        // [initializer].
+        // p-tags on a WakeUp identify the AUTHORS of the referenced events —
+        // the people whose events are the subject of the wake-up and who should
+        // come online to handle new activity on them. Callers can add extra
+        // e/p tags via [initializer] when waking up about multiple events.
         fun build(
             about: EventHintBundle<Event>,
             createdAt: Long = TimeUtils.now(),
@@ -79,7 +79,7 @@ class WakeUpEvent(
         ) = eventTemplate(KIND, content, createdAt) {
             alt(ALT_DESCRIPTION)
             about(about)
-            notify(about.event.tags.taggedUsers())
+            notify(about.toPTag())
             kind(about.event.kind)
             initializer()
         }