Compiled documentation examples

Every file here is real TypeScript, type-checked in CI against the published @verdaccio/core (pnpm --filter @verdaccio/website check:examples), and embedded into the docs with raw-loader so there is exactly one copy of each example.

The point is that an example cannot drift: if a type is renamed or removed upstream, the build fails with a compiler error instead of shipping as documentation. That is what happened to IPluginMiddleware, IPluginAuth, IPluginStorage, IPackageStorage, IStorageManager and IPlugin, which these pages documented for years after they stopped existing (verdaccio/verdaccio#5515).

When adding an example:

1. Write it here as a .ts file that compiles.
2. Import it in the page with !!raw-loader! and render it in a <CodeBlock>.
3. Never paste the code into the markdown as well.

Bumping @verdaccio/core is how the docs follow the latest release; Renovate does it, and a contract change shows up as a red build.

The one thing this cannot cover is the 6.x callback storage contract: it is not published as a type anywhere. The StoragePlugin of verdaccio@6 is pluginUtils.Storage<Config> | any, and the | any is what lets its callback calls type-check. That half of plugin-storage.md stays hand-written, which is safe because 6.x is in maintenance and the contract no longer moves.