docs: add npm badges and stable quick start to README #14

Problem

The TypeScript README still opens with prepublication candidate instructions even though session-peer@0.1.0 is publicly verified and latest points to it. It also lacks the npm version/download and CI badges used in the Python session-peer and agy-cli-usage README introductions.

Scope

• Make README.md a clear entry point for the published TypeScript package: npm version, weekly/monthly downloads, CI, supported Node, and MIT badges linked to their sources.
• Put the stable npm install and a safe first list/--dry-run example near the top. Keep source builds and release/operator detail below the user path.
• Preserve the exact TypeScript feature boundary, native-dependency requirements, JSON output contract, and Python CLI PATH coexistence guidance. Do not reuse the Python README's live demo or feature claims for this client.
• Align localized READMEs where publication/install status changes, without changing runtime or npm publication state.

Acceptance criteria

• Badge URLs point to session-peer on npm and this repository's CI/license. The npm downloads API currently returns 404 for this newly published package, so the dynamic download badges may show a temporary "package not found or too new" state until its statistics are indexed; document that state honestly.
• The English README no longer describes stable 0.1.0 as unpublished or sends users to the preview as the primary install.
• The four README contract checker and Markdown links pass; the diff contains documentation only.

References: Python README, agy-cli-usage README, Shields npm downloads.