docs: add Antigravity editor support

[muhammetakkurtt]

Add explicit documentation for configuring Apify MCP Server with the Antigravity editor manually.

---

Note

Introduces explicit Antigravity support and setup in the AI build guide.

• Adds Antigravity to recommended AI assistants and Quick Start steps
• New Antigravity tab with manual MCP server configuration (JSON using npx @apify/actors-mcp-server and APIFY_TOKEN)
• Updates references so the prompt/instructions include Antigravity alongside Cursor, Claude Code, and VS Code

^{Written by Cursor Bugbot for commit b5df9bb. Configure here.}