Adds POST /admin/posts/feature, POST /admin/posts/unfeature
(both auth-required, admin-checked inside controller via the
use case's ForbiddenException), and public GET /posts/featured.
Post serialization now includes featureSlot.
Wires PostController (recent, show, create, delete, listByUser)
and CommentController (listForPost, create, delete) to the
existing use cases. Posts and comments expose author display
names alongside user IDs. CommentRepository binding added to
RepositoryServiceProvider.
Wires AuthController (signup, confirmEmail, login, me, logout)
to the existing auth use cases. Routes mounted under /api with
AuthMiddleware on logout/me. RepositoryServiceProvider gains
EmailConfirmationToken and Post bindings; AppServiceProvider
binds the Emailer/EmailFactory and constructs SignupUser with
the configured from-address.
