docs(ai-agents): add Antigravity IDE vibe coding best practices

[beginwebdev2002]

Creates a new documentation file docs/antigravity-ide-vibe-coding.md per user request.

This document serves as a guide for using AI Agents within the Antigravity IDE, following all SEO, styling, and structural constraints:

• SEO Frontmatter: Description and tags focusing on AI agents and vibe coding.
• LSI Keywords: H1/H2 headers structured around context window management and memory strategies.
• Visuals: Centered HTML logo, Mermaid flowchart mapping the vibe coding workflow (using restricted classDef), and a Markdown table for memory strategies.
• Checklists: Concludes with a practical "Production-Ready Actionable Checklist".

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PR created automatically by Jules for task 13591503728348350933 started by @beginwebdev2002

[google-labs-jules]

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