Add manual E2E test workflow for Gemini CLI and update model mappings

- Add new GitHub Actions workflow for manual E2E testing of Gemini CLI
  - Supports multiple model options (flash, pro, 3-flash)
  - Configurable test prompt and verbose mode
  - Tests both JavaScript and Rust implementations
  - Gracefully handles missing API keys or Gemini CLI
  - Generates test summary in workflow output

- Update model mappings for Gemini CLI:
  - Add 'lite' alias for gemini-2.5-flash-lite model
  - Add '3-pro' alias for gemini-3-pro-preview model
  - Update '3-flash' to use gemini-3-flash-preview (correct naming)
  - Add comments organizing models by generation

- Update tests for new model mappings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: konard