Expose Replay MCP widgets in Codex plugin

[BLamy]

Summary

• Expose Replay MCP directly from the Codex plugin by shipping .mcp.json and declaring mcpServers in the Codex plugin manifest.
• Keep the connected Replay app entry for app-level compatibility while routing analysis tools through https://dispatch.replay.io/mcp.
• Update Codex plugin README/copy to explain Replay MCP widget support and structuredContent rendering.
• Add shared agent guidance to prefer rendered Replay inspector widgets when available.

Demo

Validation

• npm run build
• npm run typecheck
• npm run validate