Address PR review: rename package to pw.binom.agui, add native KMP targets, fix native event serialization

- Rename module package com.agui -> pw.binom.agui (dirs + code + root group)
- Expand KMP targets on all modules: jvm + macOS/ios/Linux/mingw (no Android)
- Server native via ktor-server-cio; client native via ktor-client-cio
- Annotate sealed interface BaseEvent with @Serializable so the sealed
  serializer resolves without reflection on Kotlin/Native (was reflection-only
  on JVM, so native tests failed with 'Serializer for class BaseEvent not found')

client/build.gradle.kts

@@ -6,6 +6,14 @@ plugins {
 kotlin {
     jvmToolchain(21)
     jvm()
+    macosX64()
+    macosArm64()
+    iosX64()
+    iosArm64()
+    iosSimulatorArm64()
+    linuxX64()
+    linuxArm64()
+    mingwX64()
 
     sourceSets {
         commonMain.dependencies {
@@ -17,6 +25,9 @@ kotlin {
         jvmMain.dependencies {
             implementation(libs.ktor.client.cio)
         }
+        nativeMain.dependencies {
+            implementation(libs.ktor.client.cio)
+        }
         commonTest.dependencies {
             implementation(kotlin("test"))
         }