[BOT ISSUE] Databricks: add missing `databricks-llama-4-maverick`, `databricks-gpt-oss-120b`, `databricks-gemma-3-12b`

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Summary

Three more Databricks Foundation Model API pay-per-token models are missing from packages/proxy/schema/model_list.json. This is a follow-up to #559 and #585, covering the next tier of high-impact missing models across different model families.

Missing Model IDs

Model ID	Underlying Model	Available Regions
databricks-llama-4-maverick	Meta Llama 4 Maverick	15+ regions (eastus, westus, etc.)
databricks-gpt-oss-120b	OpenAI GPT-OSS 120B	15+ regions
databricks-gemma-3-12b	Google Gemma 3 12B	15+ regions

Details

All three models are available across the majority of Databricks regions in both pay-per-token and provisioned throughput tiers. They represent three distinct model families (Meta, OpenAI open-source, Google) and are among the most widely deployed models on the Databricks platform.

Suggested entries

"databricks-llama-4-maverick": {
  "format": "openai",
  "flavor": "chat",
  "displayName": "Llama 4 Maverick",
  "available_providers": ["databricks"]
},
"databricks-gpt-oss-120b": {
  "format": "openai",
  "flavor": "chat",
  "displayName": "OpenAI GPT-OSS 120B",
  "available_providers": ["databricks"]
},
"databricks-gemma-3-12b": {
  "format": "openai",
  "flavor": "chat",
  "displayName": "Google Gemma 3 12B",
  "available_providers": ["databricks"]
}

Pricing omitted per Databricks provider constraints (no stable public per-model pricing).

Additional missing Databricks models (not covered in #559, #585, or here)

• databricks-claude-sonnet-4-5, databricks-claude-opus-4-6, databricks-claude-opus-4-5, databricks-claude-opus-4-1, databricks-claude-sonnet-4
• databricks-gpt-oss-20b
• databricks-qwen3-next-80b-a3b-instruct, databricks-qwen35-122b-a10b

Verification checklist

• Cross-source: Model IDs confirmed on Azure Databricks foundation model overview (regional availability table, updated 2026-05-19) and AWS Databricks supported models page
• Recent commits: Not covered by any recent commit to model_list.json
• ID format: Follows existing databricks-<model> naming convention
• Existing issues: Not covered by [BOT ISSUE] Databricks: add missing databricks-claude-opus-4-7, databricks-claude-sonnet-4-6, databricks-gpt-5-5 #559 or [BOT ISSUE] Databricks: add missing databricks-gpt-5-5-pro, databricks-gemini-3-5-flash, databricks-gpt-5-4-mini #585