Web support for the Website service (#17)

This PR contains the work done to introduce a new Web Swift package that provides a reusable, declarative way to register route controllers on a Hummingbird router, then adopt it in the Website service.

To provide further details about the work:

* Web package
  * The `RouterController` protocol — a Sendable protocol to group controllers behind one `routes` property.
  * The `RouteCollectionBuilder`  — a result builder that collects controllers' route collections into a stack, with full support for optionals, conditionals, and arrays.
  * The `addController(_:)` method — a `RouterMethods` extension letting controllers be listed declaratively and adding each one's routes at the router root.

* Website service
  * Added Web as a dependency of the _WebsiteLibrary_ target.
  * Conformed the `RootController` and `HealthController`controllers to the `RouterController` protocol.
  * Updated the `App+Build` extension to to use the cleaner `router.addController { … }` instead.

Reviewed-on: rock-n-code/loud-amsterdam#17
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Services/Website/Sources/Library/Public/Controllers/RootController.swift

@@ -1,17 +1,20 @@
 import Hummingbird
+import Web
 
 /// Serves the website's root routes.
 ///
-/// The controller exposes its routes as a `RouteCollection` so they can be added to a router
-/// (or a sub-group) by the application that composes it:
+/// The controller exposes its routes through its `RouterController` conformance, so the
+/// application that composes it registers them declaratively:
 ///
 /// ```swift
-/// router.addRoutes(RootController<AppRequestContext>().routes)
+/// router.addController {
+///     RootController<AppRequestContext>()
+/// }
 /// ```
 ///
 /// - Note: `Context` is the request context the routes are resolved against, and must match the
 ///   context of the router the routes are added to.
-public struct RootController<Context: LocalizedRequestContext>: Sendable {
+public struct RootController<Context: LocalizedRequestContext> {
 
     // MARK: Properties
 
@@ -25,12 +28,14 @@ public struct RootController<Context: LocalizedRequestContext>: Sendable {
         self.responses = .init { IndexPage(locale: $0) }
     }
 
-    // MARK: Computed
+}
+
+// MARK: - RouteController
+
+extension RootController: RouterController {
+
+    // MARK: Properties
 
-    /// The routes served by the controller.
-    ///
-    /// Serves a `GET` request for the root path (`/`) by rendering the ``IndexPage`` in the
-    /// language negotiated for the request.
     public var routes: RouteCollection<Context> {
         let routes = RouteCollection(context: Context.self)