feat: Add Gemini 3 models and remove deprecated legacy models

[KarthiDreamr]

This PR adds support for the new Gemini 3 models and cleans up deprecated legacy Gemini models (1.5, 1.0, pro-vision).

Model Values Source

https://ai.google.dev/gemini-api/docs/pricing
https://ai.google.dev/gemini-api/docs/models#gemini-3-pro-image-preview

Changes

New Models Added

• gemini-3-flash-preview
• gemini-3-pro-preview
• gemini-3-pro-image-preview

Deprecated Models Removed

• gemini-1.5 family (flash, flash-8b, pro, etc.)
• gemini-1.0 / gemini-pro
• gemini-pro-vision

Configuration Updates

• Updated defaultModels in config to include Gemini 3.
• Updated googleModels token limits in tokens.ts.
• Updated pricing in tx.js.
• Updated .env.example.
• Updated tests to use gemini-2.5 models instead of deprecated gemini-1.5/gemini-pro.

[KarthiDreamr]

Test code might need slight tweak as 1.x models are removed, thanks

Summary of all failing tests
FAIL src/endpoints/google/llm.spec.ts
● getSafetySettings › should map OFF to BLOCK_NONE for Gemini 1.x models

expect(received).toContainEqual(expected) // deep equality

Expected value: {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_NONE"}
Received array: [{"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "OFF"}, {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "HARM_BLOCK_THRESHOLD_UNSPECIFIED"}, {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "HARM_BLOCK_THRESHOLD_UNSPECIFIED"}, {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "HARM_BLOCK_THRESHOLD_UNSPECIFIED"}, {"category": "HARM_CATEGORY_CIVIC_INTEGRITY", "threshold": "BLOCK_NONE"}]

  743 |     const settings = getSafetySettings('gemini-2.5-flash');
  744 |
> 745 |     expect(settings).toContainEqual({
      |                      ^
  746 |       category: 'HARM_CATEGORY_SEXUALLY_EXPLICIT',
  747 |       threshold: 'BLOCK_NONE',
  748 |     });

  at Object.toContainEqual (src/endpoints/google/llm.spec.ts:745:22)

Test Suites: 1 failed, 78 passed, 79 total
Tests: 1 failed, 1 skipped, 2053 passed, 2055 total
Snapshots: 0 total
Time: 101.748 s
Ran all test suites.
npm error Lifecycle script test:ci failed with error:
npm error code 1
npm error path /home/runner/work/LibreChat/LibreChat/packages/api
npm error workspace @librechat/api@1.7.22
npm error location /home/runner/work/LibreChat/LibreChat/packages/api
npm error command failed
npm error command sh -c jest --coverage --ci --testPathIgnorePatterns=".*integration.|.*helper."
Error: Process completed with exit code 1.