refactor(quartz): dedicated NutzapEvent.buildToUser for profile nutzaps

Restores the non-null zappedEvent on NutzapEvent.build and adds a
separate buildToUser builder (p tag only, no e/k tags) for nutzaps that
target a profile instead of an event — mirroring NIP-57's profile zap
convention. CashuWalletOps.sendNutzap dispatches between the two.

https://claude.ai/code/session_01UERRsbDoRPz46Qx5HCXgAa

amethyst/src/main/java/com/vitorpamplona/amethyst/model/nip60Cashu/CashuWalletOps.kt

@@ -602,9 +602,10 @@ class CashuWalletOps(
      *
      * Spends [available] proofs at [mintUrl] to produce P2PK-locked outputs
      * worth [amountSats] for [recipientPubKey]'s [recipientP2pkPubkeyHex].
-     * Publishes a kind:9321 with the locked proofs + message, rolls leftover
-     * change into a new kind:7375, NIP-09-deletes the source token events,
-     * and records the spend in kind:7376.
+     * Publishes a kind:9321 with the locked proofs + message (referencing
+     * [zappedEvent], or p-tag-only when null for a profile nutzap), rolls
+     * leftover change into a new kind:7375, NIP-09-deletes the source token
+     * events, and records the spend in kind:7376.
      *
      * Throws if `available` doesn't sum to at least [amountSats].
      */
@@ -637,14 +638,24 @@ class CashuWalletOps(
         // Build the kind:9321 first so we have its id to reference from history.
         val proofJsons = swap.send.map { nutzapProofJson.encodeToString(NutzapProofJson.serializer(), it.toNutzapJson()) }
         val nutzapTemplate =
-            NutzapEvent.build(
-                message = message,
-                proofs = proofJsons,
-                mintUrl = mintUrl,
-                unit = "sat",
-                zappedEvent = zappedEvent,
-                recipientPubKey = recipientPubKey,
-            )
+            if (zappedEvent != null) {
+                NutzapEvent.build(
+                    message = message,
+                    proofs = proofJsons,
+                    mintUrl = mintUrl,
+                    unit = "sat",
+                    zappedEvent = zappedEvent,
+                    recipientPubKey = recipientPubKey,
+                )
+            } else {
+                NutzapEvent.buildToUser(
+                    message = message,
+                    proofs = proofJsons,
+                    mintUrl = mintUrl,
+                    unit = "sat",
+                    recipientPubKey = recipientPubKey,
+                )
+            }
         val nutzapEvent = signer.sign(nutzapTemplate)
         publish(nutzapEvent)
         // kind:9321 is out — recipient's auto-redeem can fire from here.

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip61Nutzaps/nutzap/NutzapEvent.kt

@@ -62,16 +62,35 @@ class NutzapEvent(
         const val KIND = 9321
         const val ALT_DESCRIPTION = "Nutzap"
 
-        /**
-         * [zappedEvent] is optional: a nutzap aimed at a profile rather than a
-         * specific event carries only the `p` tag (the `e`/`k` tags are omitted).
-         */
         fun build(
             message: String,
             proofs: List<String>,
             mintUrl: String,
             unit: String,
-            zappedEvent: EventHintBundle<out Event>?,
+            zappedEvent: EventHintBundle<out Event>,
+            recipientPubKey: HexKey,
+            createdAt: Long = TimeUtils.now(),
+            initializer: TagArrayBuilder<NutzapEvent>.() -> Unit = {},
+        ) = eventTemplate(KIND, message, createdAt) {
+            alt(ALT_DESCRIPTION)
+            proofs(proofs)
+            mintUrl(mintUrl)
+            unit(unit)
+            zappedEvent(zappedEvent)
+            zappedEventKind(zappedEvent.event.kind)
+            recipient(recipientPubKey)
+            initializer()
+        }
+
+        /**
+         * Nutzap aimed at a profile rather than a specific event: carries only
+         * the `p` tag (no `e`/`k` tags), mirroring NIP-57's profile zaps.
+         */
+        fun buildToUser(
+            message: String,
+            proofs: List<String>,
+            mintUrl: String,
+            unit: String,
             recipientPubKey: HexKey,
             createdAt: Long = TimeUtils.now(),
             initializer: TagArrayBuilder<NutzapEvent>.() -> Unit = {},
@@ -80,10 +99,6 @@ class NutzapEvent(
             proofs(proofs)
             mintUrl(mintUrl)
             unit(unit)
-            if (zappedEvent != null) {
-                zappedEvent(zappedEvent)
-                zappedEventKind(zappedEvent.event.kind)
-            }
             recipient(recipientPubKey)
             initializer()
         }