MCP surface for tkn CLI

Summary

Expose tkn as an MCP (Model Context Protocol) server, enabling direct integration with AI agents like Claude Code without requiring shell execution. This could consolidate the standalone tekton mcp-server into the tkn binary itself.

Proposal

• Expose tkn operations as MCP tools via JSON-RPC
• Support tkn mcp serve or similar to start MCP server mode
• Maintain CLI, kubectl plugin, and MCP surfaces from a single binary
• Support environment variable credential injection for headless execution

Acceptance Criteria

• tkn can serve as an MCP server exposing Tekton operations as tools
• MCP tools cover core operations (list, describe, create, start, logs)
• Single binary serves CLI, kubectl plugin, and MCP interfaces
• Migration path documented for standalone tekton mcp-server users

Context

Part of #2849 — making tkn agent-friendly.

Note: A standalone tekton mcp-server already exists. This epic would evaluate consolidating that into tkn itself to reduce deployment complexity. Deprecation timeline would be coordinated with the Tekton community.

/kind feature

Start by reviewing the standalone tekton mcp-server and the proposed tkn mcp serve entry point, with context from #2849. Define the integration scope around the listed core operations and credential injection. Done means the acceptance criteria are met and the migration path for standalone users is documented.