Improve onboarding and publish npm and Docker installs to the MCP Registry

[marcomoauro]

Summary

• move a complete NPX quick start and credential retrieval instructions to the top of the README
• add official MCP Registry metadata for both npm and Docker installations
• publish npm and registry metadata in separate rerunnable jobs with least-privilege OIDC permissions
• wait for the independently built versioned Docker image and verify its ownership label before registry publication
• verify the pinned mcp-publisher download against its release checksum
• document the release invariants in CLAUDE.md
• add a lower-friction issue form that still requires reproducible details and secret sanitization
• improve npm discovery keywords

Verification

• 748 tests pass on Node.js 22
• 748 tests pass on Node.js 24.19.0
• mcp-publisher 1.8.1 validates the generated npm and OCI metadata against the official registry
• a local Docker build contains the required io.modelcontextprotocol.server.name ownership label
• actionlint validates all GitHub Actions workflows
• both YAML files and all README JSON examples parse
• npm pack includes the required mcpName metadata

Release note

The official registry validates ownership against the published npm package and Docker image. The first registry entry will therefore be created automatically by the next version tag, after both artifacts containing their new ownership metadata are available. Repository topics cannot be represented in a pull request and can be added after merge.