Description:
Currently, the Vertex AI API version (e.g., v1beta1) is either hardcoded or relying on the SDK default across multiple model files (models/veo.py, models/image_models.py, etc.).

We should centralize this configuration to ensure consistency and make upgrades easier for users that want to explicitly set a version (v1beta1, v1, etc.).

Proposed Changes:

1. Update config/default.py:
   Add a new configuration variable to the Default class:

   VERTEX_API_VERSION: str = os.environ.get("VERTEX_API_VERSION", "v1beta1")

2. Refactor Model Clients:
   Update all genai.Client instantiations to use this config value.

   client = genai.Client(
       # ...
       http_options={'api_version': config.VERTEX_API_VERSION}
   )

Affected Files:

• config/default.py
• models/image_models.py
• models/veo.py
• models/vto.py
• models/upscale.py
• models/character_consistency.py
• models/model_setup.py