feat(google-vertex): update model YAMLs [bot]

[harshiv-26]

Auto-generated by poc-agent for provider google-vertex.

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Note

Low Risk
Adds/updates a single provider YAML with pricing, limits, and capability flags; no runtime logic changes. Risk is limited to potential downstream parsing/behavior changes if consumers assume missing fields.

Overview
Updates the google/gemma-4-26b-a4b-it-maas Google Vertex model YAML to include pricing, capability flags (e.g., function_calling, structured_output, system_messages), and token/context limits.

Also declares supported input/output modalities, supportedModes, status, sources, a max_tokens param constraint, and enables thinking: true while setting mode: chat.

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