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>

Packages/Web/Sources/Public/Protocols/RouterController.swift

@@ -0,0 +1,32 @@
+import Hummingbird
+
+/// A type exposing its endpoints as a route collection ready to be added to a router.
+///
+/// Conforming controllers group related endpoints behind a single ``routes`` property,
+/// so the application composes them declaratively with ``Hummingbird/RouterMethods/addController(_:)``:
+///
+/// ```swift
+/// struct HealthController<Context: RequestContext>: RouterController {
+///     var routes: RouteCollection<Context> {
+///         RouteCollection(context: Context.self)
+///             .get("health") { _, _ in HTTPResponse.Status.ok }
+///     }
+/// }
+///
+/// router.addController {
+///     HealthController<AppRequestContext>()
+/// }
+/// ```
+public protocol RouterController<Context>: Sendable {
+    
+    // MARK: Associated types
+    
+    /// The request context the controller's routes operate on.
+    associatedtype Context: RequestContext
+    
+    // MARK: Properties
+    
+    /// The collection of routes the controller exposes.
+    var routes: RouteCollection<Context> { get }
+    
+}