feat: plugin schema extension for mcp plugins

[Pratham-Mishra04]

Summary

Briefly explain the purpose of this PR and the problem it solves.

Changes

• What was changed and why
• Any notable design decisions or trade-offs

Type of change

• Bug fix
• Feature
• Refactor
• Documentation
• Chore/CI

Affected areas

• Core (Go)
• Transports (HTTP)
• Providers/Integrations
• Plugins
• UI (Next.js)
• Docs

How to test

Describe the steps to validate this change. Include commands and expected outcomes.

# Core/Transports
go version
go test ./...

# UI
cd ui
pnpm i || npm i
pnpm test || npm test
pnpm build || npm run build

If adding new configs or environment variables, document them here.

Screenshots/Recordings

If UI changes, add before/after screenshots or short clips.

Breaking changes

• Yes
• No

If yes, describe impact and migration instructions.

Related issues

Link related issues and discussions. Example: Closes #123

Security considerations

Note any security implications (auth, secrets, PII, sandboxing, etc.).

Checklist

• I read docs/contributing/README.md and followed the guidelines
• I added/updated tests where appropriate
• I updated documentation where needed
• I verified builds succeed (Go and UI)
• I verified the CI pipeline passes locally if applicable