ci: publish-on-release workflow + maven-publish (caffeine)

- .gitea/workflows/build.yml: on release -> subochev/devops/publish -> caffeine
- maven-publish wired into api/client/server (KMP per-target publications)
- root: caffeine repo (nexus.xx) + pom; version via gradle.properties, overridable by -Pversion

build.gradle.kts

@@ -1,3 +1,5 @@
+import org.gradle.api.publish.maven.MavenPublication
+
 plugins {
     alias(libs.plugins.kotlin.multiplatform) apply false
     alias(libs.plugins.kotlin.serialization) apply false
@@ -5,5 +7,29 @@ plugins {
 
 allprojects {
     group = "pw.binom.agui"
-    version = "0.1.0-SNAPSHOT"
+}
+
+subprojects {
+    plugins.withId("maven-publish") {
+        extensions.configure<PublishingExtension>("publishing") {
+            publications.withType<MavenPublication>().configureEach {
+                pom {
+                    name.set(project.name)
+                    description.set("AG-UI (Agent-User Interface) protocol implementation")
+                    url.set("https://github.com/ag-ui-protocol/ag-ui")
+                }
+            }
+            repositories {
+                maven {
+                    name = "caffeine"
+                    url = uri("http://nexus.xx/repository/caffeine/")
+                    isAllowInsecureProtocol = true
+                    credentials {
+                        username = (project.findProperty("binom.repo.user") as String?) ?: System.getenv("BINOM_REPO_USER").orEmpty()
+                        password = (project.findProperty("binom.repo.password") as String?) ?: System.getenv("BINOM_REPO_PASSWORD").orEmpty()
+                    }
+                }
+            }
+        }
+    }
 }