feat: Enable global default `model.json` with all the fallback properties

[0xSage]

Problem A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

Success Criteria

• It should be clearly accessible in ./models folder.
• Location suggestions: ./models/defaults ./models/global ./models/common
• It should be clearly named to accommodate future model formats:
• i.e. default_model.json, default_gguf_model.json

Additional context Add any other context or screenshots about the feature request here. Blocking: #1028