build: declare singleVariant("release") to register publish component

AGP 7.1+ does not automatically register the release SoftwareComponent
for maven-publish. Must explicitly opt in via android { publishing {
singleVariant("release") } } so that components.release is available
in afterEvaluate.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sdk-core/build.gradle.kts

@@ -23,6 +23,10 @@ android {
     buildFeatures {
         compose = true
     }
+
+    publishing {
+        singleVariant("release")
+    }
 }
 
 dependencies {

sdk-im/build.gradle.kts

@@ -17,6 +17,10 @@ android {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
     }
+
+    publishing {
+        singleVariant("release")
+    }
 }
 
 dependencies {

sdk-push/build.gradle.kts

@@ -17,6 +17,10 @@ android {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
     }
+
+    publishing {
+        singleVariant("release")
+    }
 }
 
 dependencies {

sdk-update/build.gradle.kts

@@ -17,6 +17,10 @@ android {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
     }
+
+    publishing {
+        singleVariant("release")
+    }
 }
 
 dependencies {