feat(vendor-gemini-cli): update gemini model version

[zwpaper]

Summary

Update gemini-3-pro-preview to gemini-3.1-pro-preview in packages/vendor-gemini-cli and packages/cli.

Test plan

• Verify the model version is updated in the code.
• Run bun check to ensure no linting issues.

🤖 Generated with Pochi | Task

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 13.55%. Comparing base (75a9940) to head (3e49634).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1305   +/-   ##
=======================================
  Coverage   13.55%   13.55%           
=======================================
  Files         680      680           
  Lines       62186    62186           
  Branches     1788     1788           
=======================================
  Hits         8432     8432           
  Misses      53476    53476           
  Partials      278      278           

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