Add MCP registry metadata (server.json + mcpName)

[jdrhyne]

Summary

• Adds server.json at the repo root and an mcpName field to package.json, the two things required to publish this server to the official MCP registry (registry.modelcontextprotocol.io).
• Namespace: io.github.PSPDFKit/nutrient-document-engine-mcp-server (GitHub-auth).
• No runtime code changed. Metadata only.

Why

Publishing once to the official registry cascades automatically to Glama, PulseMCP, and mcp.so. Today this server has no server.json, so it isn't in the official registry.

Before publishing (maintainer checklist)

brew install mcp-publisher
mcp-publisher login github        # needs push access to PSPDFKit
mcp-publisher publish --dry-run
mcp-publisher publish

Please confirm at dry-run time:

• Version alignment — server.json and package.json are both 0.0.1, but npm latest is 0.0.2. Reconcile these (bump repo to the version you'll publish) before publishing; the registry validates that server.json version matches the published npm version.
• $schema date is current (dry-run flags if stale).
• env vars complete — I included DOCUMENT_ENGINE_BASE_URL (required) and DOCUMENT_ENGINE_API_AUTH_TOKEN (required/secret). ACTIVATION_KEY is a Document Engine deployment setting, not an MCP client env, so it's intentionally excluded — add it if the server itself reads it.

Test plan

• package.json and server.json both parse as valid JSON.
• Diff is metadata-only (package.json +1 line, new server.json).
• mcp-publisher publish --dry-run passes (run by a maintainer).