feat: add NIP-77 negentropy sync support

Add support for NIP-77 (Negentropy Syncing) protocol messages using
the negentropy-kmp library for efficient set reconciliation between
client and relay.

New files:
- NegOpenCmd, NegMsgCmd, NegCloseCmd: Client-to-relay commands
- NegMsgMessage, NegErrMessage: Relay-to-client messages
- NegentropySession: Client-side reconciliation orchestrator
- NegentropyServerSession: Server-side reconciliation handler
- NegentropyManager: High-level sync manager with listener callbacks

Updated serializers:
- Jackson MessageSerializer/Deserializer for NEG-MSG, NEG-ERR
- Jackson CommandSerializer/Deserializer for NEG-OPEN, NEG-MSG, NEG-CLOSE
- Kotlin MessageKSerializer/CommandKSerializer for all NIP-77 types

Compatible with strfry relay's negentropy implementation via the
negentropy-kmp library which implements the same Protocol V1 spec.

https://claude.ai/code/session_01Dc6W1G1jURAAR9kzyVvk6g

gradle/libs.versions.toml

@@ -41,6 +41,7 @@ materialIconsExtended = "1.7.3"
 media3 = "1.9.3"
 mockk = "1.14.9"
 kotlinx-coroutines-test = "1.10.2"
+negentropyKmp = "1.0.1"
 netUrlencoderLibVersion = "1.6.0"
 navigationCompose = "2.9.7"
 okhttp = "5.3.2"
@@ -156,6 +157,7 @@ markdown-ui-material3 = { group = "com.github.vitorpamplona.compose-richtext", n
 mockk = { group = "io.mockk", name = "mockk", version.ref = "mockk" }
 mockk-android = { group = "io.mockk", name = "mockk-android", version.ref = "mockk" }
 kotlinx-coroutines-test = { group = "org.jetbrains.kotlinx", name = "kotlinx-coroutines-test", version.ref = "kotlinx-coroutines-test"}
+negentropy-kmp = { module = "com.vitorpamplona.negentropy:kmp-negentropy", version.ref = "negentropyKmp" }
 net-thauvin-erik-urlencoder-lib = { module = "net.thauvin.erik.urlencoder:urlencoder-lib", version.ref = "netUrlencoderLibVersion" }
 okhttp = { group = "com.squareup.okhttp3", name = "okhttp", version.ref = "okhttp" }
 okhttpCoroutines = { group = "com.squareup.okhttp3", name = "okhttp-coroutines", version.ref = "okhttp" }