feat(distribution): tighten public distribution contract

[xiaojiou176]

Summary

• add a canonical distribution contract and public distribution status page
• artifactize the read-only MCP surface with a machine-readable manifest and wrapper-first startup story
• align starter configs, builder/package metadata, and release truth wording with the current shipped vs deferred boundary

Verification

• npm run docs:check
• bash scripts/check_repo_hygiene.sh
• printf '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}\n' | bash scripts/run_readonly_mcp.sh