Shared HTML template for the Website service (#22)

This PR contains the work done to define a `Page` protocol that extracts the HTML scaffolding that `IndexPage` and `ErrorPage` pages duplicated, so every page of the website declares only what makes it unique — its content, title, and assets — while the document structure lives in one place. Also cleans up imports across the workspace.

Reviewed-on: rock-n-code/loud-amsterdam#22
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Services/Website/Sources/Library/Internal/Pages/ErrorPage.swift

@@ -3,12 +3,12 @@ import Foundation
 import Localization
 
 /// The HTML page rendered for a not-found response, with its text localized to a given locale.
-struct ErrorPage: HTMLDocument, Sendable {
+struct ErrorPage {
 
     // MARK: Properties
 
     /// The locale the page content is localized to.
-    private let locale: Locale
+    let locale: Locale
 
     /// Resolves the page's text from the bundled String Catalog for the page's ``locale``.
     private let localize: Localize
@@ -23,45 +23,31 @@ struct ErrorPage: HTMLDocument, Sendable {
         self.locale = locale
         self.localize = .init(bundle: .module)
     }
+}
 
-    // MARK: Document
+// MARK: Page
 
-    /// The page's content: a localized heading and explanatory message, followed by the error and shared scripts.
-    var body: some HTML {
+extension ErrorPage: Page {
+
+    // MARK: Properties
+
+    var content: some HTML {
         h1 {
             localize("error.heading", locale: locale)
         }
         p {
             localize("error.message", locale: locale)
         }
-        script(.src(StaticFile.error.urlPath(for: .js))) {}
-        script(.src(StaticFile.shared.urlPath(for: .js))) {}
     }
 
-    /// The metadata and stylesheet links placed in the document head.
-    var head: some HTML {
-        meta(.charset(.utf8))
-        meta(
-            .name(.viewport),
-            .content("width=device-width, initial-scale=1")
-        )
-        link(
-            .rel(.stylesheet),
-            .href(StaticFile.shared.urlPath(for: .css))
-        )
-        link(
-            .rel(.stylesheet),
-            .href(StaticFile.error.urlPath(for: .css))
-        )
+    var scripts: [StaticFile] {
+        [.error, .shared]
     }
 
-    /// The document language, derived from the page's locale and falling back to the default language.
-    var lang: String {
-        locale.language.languageCode?.identifier
-            ?? LanguageList(bundle: .module).default
+    var stylesheets: [StaticFile] {
+        [.shared, .error]
     }
 
-    /// The localized document title.
     var title: String {
         localize("error.title", locale: locale)
     }