ci: enable npm auto-publish + fix MCP Registry description length

[jakezwang]

Two release-automation fixes:

1. server.json — shorten description to ≤100 chars (the MCP Registry rejects longer). The registry entry io.github.argon-lab/argon is already live at v2.0.1; this syncs master so future release-triggered publishes don't fail validation.
2. release.yml — enable the publish-npm job so a tag push auto-publishes argonctl to npm.

Action required to activate #2: add an NPM_TOKEN repo secret — an npm Automation token (or granular with 2FA bypass) that owns argonctl, so CI publishes without an OTP:

gh secret set NPM_TOKEN --repo argon-lab/argon   # paste the token (hidden)

After that, cutting a release ( bump version → tag vX.Y.Z) auto-builds binaries and publishes npm; then run the publish-mcp workflow (or dispatch it) to register the new version.