Simplify plugin installation and runtime loading around package-manager-owned dependencies, with Jiti reserved for local/TS fallback paths.
Also scans npm plugin install roots so hoisted transitive dependencies are covered by dependency denylist and node_modules symlink checks.
* test(ci): route plugin prerelease coverage to plugin shard
* test(ci): add plugin prerelease suite to CI
* fix(ci): preserve pnpm path in plugin prerelease shard
* fix(ci): avoid inheriting secrets for plugin prerelease suite
