Harden Macaly Code for OpenAI plugin submission

[petrbrzek]

What changed

• align the Macaly Code manifest with OpenAI directory requirements
• rename the MCP configuration to .mcp.json and update all references
• validate listing fields, categories, required HTTPS URLs, and final plugin layout
• add OpenAI submission notes with test cases, annotation rationale, release notes, and reviewer checklist
• clarify Codex installation, OAuth, and ChatGPT restart instructions

Why

The existing marketplace plugin was a solid base, but its listing metadata, MCP filename, validation coverage, and submission materials needed hardening before an official OpenAI directory submission.

Impact

This changes packaging and documentation only. The production MCP endpoint and tool behavior remain unchanged.

Verification

• bun run build
• git diff --check

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