Update gemini/genai doc: models are 2 generations behind (2.5 → 3.1)

[kc9611]

Summary

The gemini/genai Python doc (content/gemini/docs/genai/python/DOC.md) recommends Gemini 2.5 models, but Google has since released Gemini 3.1 (as of March 2026). The doc is ~2 generations behind.

What's wrong

Model recommendations are outdated

What the doc says	What it should be (March 2026)
gemini-2.5-flash (General)	gemini-3-flash-preview
gemini-2.5-pro (Reasoning)	gemini-3.1-pro-preview (released Feb 19, 2026)
gemini-2.0-flash (acceptable)	gemini-3.1-flash-lite (released March 3, 2026)
gemini-2.5-flash-image-preview (Image editing)	gemini-3.1-flash-image

Deprecated models list is incomplete

The doc only lists 1.5 series as deprecated. The following should also be listed:

• All 2.x models (gemini-2.0-flash, gemini-2.0-pro)
• All 2.5 models (gemini-2.5-flash, gemini-2.5-pro)
• gemini-3-pro-preview (shut down March 9, 2026 — users told to migrate to 3.1 Pro)

SDK version is outdated

• Doc says: 1.56.0
• Latest on PyPI: 1.67.0 (released March 12, 2026)

What's still correct

• The SDK import pattern (from google import genai)
• Client initialization (client = genai.Client())
• API call patterns (client.models.generate_content(...))
• Streaming (generate_content_stream)
• Tool/function calling, structured outputs, system instructions
• Image generation with Imagen, video generation with Veo
• The deprecation of google-generativeai (legacy SDK)

Suggested changes to content/gemini/docs/genai/python/DOC.md

1. Update frontmatter versions to 1.67.0 and updated-on to current date, bump revision
2. Replace model recommendations:
   • General → gemini-3-flash-preview
   • Reasoning → gemini-3.1-pro-preview
   • Cost-efficient → gemini-3.1-flash-lite
3. Update deprecated models list to include all 2.x and 2.5 series
4. Update image editing model to gemini-3.1-flash-image
5. Update all code examples to use the new model IDs

References

• Gemini 3.1 Pro announcement
• Gemini 3.1 Flash-Lite announcement
• Gemini 3 Pro deprecation
• google-genai on PyPI
• Google AI Models page