docs(npm): npm badge, pnpm/bun install commands, homepage/bugs links

[Alex-Wengg]

What

• Add npm version badge to the README (links to the package).
• Show pnpm add and bun add alongside npm i, plus an explicit "on npm" link.
• Add homepage and bugs fields to npm/package.json so the npm sidebar surfaces the GitHub README and issues (repository link was already present).

Notes

• homepage/bugs reach the live npm page on the next npm publish.
• The GitHub repo description was broadened separately (no longer Electron-only).