docs: [vertexai] Add deprecation note in README and pom (#11638)

Author: jaycee-li

java-vertexai/README.md

@@ -1,5 +1,13 @@
 # Google Vertex AI SDK for Java
 
+> **Note:** The `com.google.cloud.vertexai.generativeai` package and its classes
+> are **deprecated as of June 24, 2025 and will be removed on June 24, 2026.**
+> Please use the
+> [Google Gen AI SDK](https://central.sonatype.com/artifact/com.google.genai/google-genai)
+> to access GenAI features. See
+> [the migration guide](https://cloud.google.com/vertex-ai/generative-ai/docs/deprecations/genai-vertexai-sdk#java)
+> for details.
+
 Java idiomatic SDK for [Vertex AI][product-docs].
 
 [![Maven][maven-version-image]][maven-version-link]

java-vertexai/google-cloud-vertexai/pom.xml

@@ -6,9 +6,22 @@
   <version>1.26.0</version><!-- {x-version-update:google-cloud-vertexai:current} -->
   <packaging>jar</packaging>
   <name>Google VertexAI API</name>
-  <description>VertexAI API Vertex AI is an integrated suite of machine learning tools and services
+  <description>Vertex AI is an integrated suite of machine learning tools and services
     for building and using ML models with AutoML or custom code. It offers both novices and experts
-    the best workbench for the entire machine learning development lifecycle.</description>
+    the best workbench for the entire machine learning development lifecycle.
+
+    --------------------------------------------------------------------------------------
+    DEPRECATION NOTICE:
+    The 'com.google.cloud.vertexai.generativeai' package and its classes are deprecated as of
+    June 24, 2025 and will be removed on June 24, 2026.
+
+    Please transition to the Google Gen AI SDK (com.google.genai:google-genai)
+    for GenAI functionality.
+
+    A detailed migration guide is available at:
+    https://cloud.google.com/vertex-ai/generative-ai/docs/deprecations/genai-vertexai-sdk#java
+    --------------------------------------------------------------------------------------
+  </description>
   <parent>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-vertexai-parent</artifactId>