Publish MCP helper packages from the tag workflow

[OkeyAmy]

Problem

DRS now has a clear no-fork adoption story for the SDK and verifier image, but the Node helper packages are still workspace packages. The first usable product path needs @drs/mcp-server and @drs/mcp-client to be installable like the rest of the stack.

What to do

• publish @drs/mcp-server and @drs/mcp-client from the release workflow
• version them with the rest of the repo on v* tags
• document the supported version matrix next to the SDK and verifier quickstart
• make released-artifact tests install the published helpers, not workspace packages

Acceptance criteria

• tagging v* publishes both helper packages to npm
• README and builder docs show the npm install path
• release CI fails if either helper package cannot be built or published
• the released-artifact test installs the published helpers and passes against the tagged verifier image

Out of scope

• Claude or Codex plugins
• new framework adapters
• Shape 2 binding parity