Add ppn version and rewrite the README around use cases

[mordamax]

Two things. ppn --version answered nothing before, and a bare number is misleading in a checkout, where package.json holds the placeholder the release rewrites at publish. And the README showed one fork example, so the no-sudo half of forking was invisible.

• ppn version reports the version plus how the copy was installed: a dist reads its release manifest, an npm install the stamped package version, a checkout falls back to git HEAD. --json for consumers.
• ppn --version / -V print the bare number.
• The spawn stamp now shares the dist-manifest reader instead of keeping its own.
• README: forking a sudo testnet vs a mainnet without sudo, with the runtime authorized at bite time.
• README: ppn bite on its own, fork resume and --clean, --pin-products, remote upgrades, the duplicate security block removed.