fix(cursor): restore plugin API key so Configure works

[runnabro]

Summary

• Restore README_API_KEY as a Cursor plugin variable and send it as Authorization: Bearer ${README_API_KEY} on the plugin MCP server, matching GitHub's plugin pattern.
• feat(plugins): cursor & refactor #7 renamed the Agent Plugins root manifest into cursor/ and deleted the Cursor manifest that already had this, which is why marketplace install has no Configure field.
• Claude and Codex stay anonymous; only the Cursor plugin and mcp-auth Cursor row change.

Test plan

• Manifest validates against Cursor's plugin schema (variables.type is object, ${README_API_KEY} is declared).
• Uninstall the marketplace ReadMe plugin (it shadows a same-named local copy), reload the window, and install from ~/.cursor/plugins/local/readme or this branch.
• Confirm Plugins → Configure shows ReadMe API key and that saving it reconnects MCP as Connected.
• execute-request against GET https://api.readme.com/v2/projects/me returns your project, not a Missing Security Schemes error.
• Claude/Codex manifests still have no Authorization header.

Made with Cursor

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with the Cursor credential declaration, interpolation, documentation, and generated skill copies aligned.

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