[BOT ISSUE] Google: add stable gemini-3.1-flash-image model (GA promotion from preview)

[github-actions]

Summary

Google has promoted gemini-3.1-flash-image to stable/GA. The catalog currently only has the preview version (gemini-3.1-flash-image-preview). The stable model ID should be added for both Google AI and Vertex AI paths.

Missing Models

Model ID	Display Name	Provider
gemini-3.1-flash-image	Gemini 3.1 Flash Image	google
publishers/google/models/gemini-3.1-flash-image	Gemini 3.1 Flash Image	vertex

Suggested Catalog Entry

"gemini-3.1-flash-image": {
  "format": "google",
  "flavor": "chat",
  "multimodal": true,
  "input_cost_per_mil_tokens": 0.5,
  "output_cost_per_mil_tokens": 3,
  "displayName": "Gemini 3.1 Flash Image",
  "supported_regions": [
    "global"
  ],
  "max_input_tokens": 131072,
  "max_output_tokens": 32768,
  "available_providers": [
    "google"
  ]
}

Sources

• Google AI Pricing — lists gemini-3.1-flash-image at $0.50 input / $3.00 output per 1M tokens
• Google AI Models — links to gemini-3.1-flash-image as a current model

Existing Catalog Reference

The catalog already has gemini-3.1-flash-image-preview (line ~6803) and publishers/google/models/gemini-3.1-flash-image-preview (line ~8727) with identical pricing. The stable version should follow the same pattern.

[github-actions]

Autofix skipped because the issue body/title did not contain parseable bot metadata for a model catalog change.