chore: update model manifest

[github-actions]

Automated model discovery run.

This PR updates components/manifests/base/core/models.json based on
probing Vertex AI endpoints. Validation passed — safe to auto-merge.

Unleash flags are synced automatically on deploy by the
sync-model-flags Job.

Diff

diff --git a/components/manifests/base/core/models.json b/components/manifests/base/core/models.json
index a8468fc..605b7d5 100755
--- a/components/manifests/base/core/models.json
+++ b/components/manifests/base/core/models.json
@@ -149,6 +149,14 @@
       "provider": "google",
       "available": false,
       "featureGated": true
+    },
+    {
+      "id": "gemini-3.5-flash",
+      "label": "Gemini 3.5 Flash",
+      "vertexId": "gemini-3.5-flash@default",
+      "provider": "google",
+      "available": false,
+      "featureGated": true
     }
   ]
 }

[ambient-code]

Manifest validation passed — auto-approved by model discovery workflow

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