Prepare npm package publishing

[BotondCsereklye]

What changed

• add a repeatable npm tarball contract check
• verify the CLI shebang, executable mode, version and bundled GUI assets
• run the full validation suite before npm publish
• document the maintainer release and registry verification process
• link the publishing guide from the README, development guide and website

Validation

• npm run prepublishOnly
• 56 tests passed
• coverage: 90.81% statements, 83.88% branches
• npm pack: 130 files, 68.6 kB
• isolated tarball installation: loopeng --version returned 0.1.0