* feat(plugins): unify source installation and simplify plugin settings
* feat(plugins): install npm sources and review CLI updates
Treat install selectors as one-time choices. Keep source identity separate from the installed revision, and resolve ordinary updates from the current upstream default. npm only acquires directories; plugin loading remains independent of npm.
* fix(plugins): preserve CLI diagnostics and exercise reviewed updates
Move new source capability coverage to real browser journeys. Update the requirements regression to exercise preview and apply, and preserve the existing duplicate-selector diagnostic across positional option scopes.
* test(plugins): remove unused pending helper
* test(plugins): pack registry fixtures with the Windows command runner
* test(plugins): assert failed client contribution setup
* docs(plugins): consolidate guides and document npm publishing
* docs(plugins): introduce publishing choices before npm instructions
* test(plugins): own browser journey cleanup in a fixture
* feat(plugins): prepare scaffolded packages for publishing
