chore(vertexai): create release (#14175)

PR created by the Librarian CLI to initialize a release. Merging this PR
will auto trigger a release.

Librarian Version: v0.8.3
Language Image:
us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/librarian-go@sha256:19bb93e8f1f916c61b597db2bad65dc432f79baaabb210499d7d0e4ad1dffe29
<details><summary>vertexai: v0.16.0</summary>

##
[v0.16.0](BenjaminKazemi/google-cloud-go@vertexai/v0.15.0...vertexai/v0.16.0)
(2026-03-13)

### Features

* Support AgentEngine for Agent Development Kit (#14168)
([e56381c](BenjaminKazemi@e56381ca))

</details>

Author: BenjaminKazemi

.librarian/state.yaml

@@ -6274,7 +6274,7 @@ libraries:
       - ^vectorsearch/apiv1/vectorsearchpb/.*$
     tag_format: '{id}/v{version}'
   - id: vertexai
-    version: 0.15.0
+    version: 0.16.0
     last_generated_commit: e8365a7f88fabe8717cb8322b8ce784b03b6daea
     apis: []
     source_roots:

vertexai/CHANGES.md

@@ -1,5 +1,11 @@
 # Changes
 
+## [0.16.0](https://github.com/googleapis/google-cloud-go/releases/tag/vertexai%2Fv0.16.0) (2026-03-13)
+
+### Features
+
+* Support AgentEngine for Agent Development Kit (#14168) ([e56381c](https://github.com/googleapis/google-cloud-go/commit/e56381ca7200c924ea54127a5d918dba548e3188))
+
 ## [0.15.0](https://github.com/googleapis/google-cloud-go/compare/vertexai/v0.14.0...vertexai/v0.15.0) (2025-06-25)