Add gemini-cli documentation page

[cmungall]

Adds comprehensive documentation for Google's Gemini CLI following the same format as the goose page and adds it to mkdocs.yml navigation.

Includes:

• YAML frontmatter with all required fields
• Description based on official Google documentation
• Key features and capabilities
• Supported models and UI information
• Navigation entry in mkdocs.yml

Fixes #18

🤖 Generated with Claude Code

[claude]

Claude finished @cmungall's task —— View job

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PR Review Complete ✅

Reviewing this PR for code quality, potential bugs, performance considerations, security concerns, and test coverage.

Todo List:

• Read repository guidelines (CLAUDE.md)
• Examine the modified mkdocs.yml file
• Locate and review the gemini-cli documentation file
• Compare with existing goose documentation for consistency
• Provide comprehensive review feedback

Review Feedback

This PR successfully adds comprehensive documentation for Google's Gemini CLI following the established patterns. Here's my detailed review:

✅ Code Quality & Best Practices

• Excellent structure: The documentation follows the exact same YAML frontmatter format as the existing goose.md file
• Consistent navigation: The mkdocs.yml entry is properly placed alphabetically between "Claude Code" and "Goose"
• Complete metadata: All required frontmatter fields are present (title, url, logo, models, ui_type, ease_of_use_for_non_technical, github)

✅ Content Quality

• Accurate description: Based on official Google documentation with appropriate technical detail
• Clear feature summary: Covers key capabilities like 1M token context window, multimodal support, and MCP integration
• Appropriate scope: Concise yet comprehensive overview suitable for the reference section

✅ Consistency with Repository Patterns

• Perfect format match: Mirrors the goose.md structure exactly
• Appropriate logo: Uses official Google favicon (32x32 format)
• Correct ease_of_use rating: Rating of 4 seems appropriate for a CLI tool (compared to Goose's 5)

✅ Technical Implementation

• Clean diff: Only adds necessary navigation entry in mkdocs.yml
• No breaking changes: Addition is purely additive
• Proper file placement: Documentation file created in correct location (docs/reference/clients/)

✅ Security & Performance

• Safe external references: Logo URL uses Google's official CDN
• No security concerns: No executable code or sensitive information
• Minimal performance impact: Single navigation entry addition

⚠️ Minor Observations

• Test coverage: No tests needed for documentation, but consider adding a link check in CI if not already present
• Logo accessibility: The Google favicon may be small for some users, but this follows the established pattern

Verdict: APPROVED ✅

This is a well-executed documentation addition that perfectly follows the repository's established patterns and provides valuable information for users interested in Google's Gemini CLI.