Added font preload links to the Page+Defaults extension in the Website library target.

Services/Website/Sources/Library/Internal/Extensions/Page+Defaults.swift

@@ -6,6 +6,16 @@ import Localization
 /// The site-wide defaults shared by every page of the website.
 extension Page {
 
+    // MARK: Constants
+
+    /// The fonts preloaded on every page: one per face the stylesheets actually render.
+    ///
+    /// Listed rather than derived from every WOFF2 in ``StaticFile/all``: a subset gated by a `unicode-range` no page reaches would add a
+    /// download that never otherwise happens. Empty until the site ships fonts of its own.
+    static var preloadedFonts: [StaticFile] {
+        []
+    }
+
     // MARK: Computed
 
     /// The document language, derived from the page's locale and falling back to the default language.
@@ -14,9 +24,29 @@ extension Page {
             ?? LanguageList().default
     }
 
-    /// The icon, manifest, and theme colour metadata shared by every page of the website.
-    @HTMLBuilder
+    /// The site-wide head metadata; a page that adds tags of its own composes ``siteMetadata`` rather than replacing it.
     var metadata: some HTML {
+        siteMetadata
+    }
+
+    /// The ``preloadedFonts`` links, then the icon, manifest, and theme colour metadata shared by every page of the website.
+    ///
+    /// A preload URL must match the stylesheet's `@font-face` source exactly — unversioned, with `crossorigin` — or the browser fetches the
+    /// font twice.
+    @HTMLBuilder
+    var siteMetadata: some HTML {
+        for file in Self.preloadedFonts {
+            link(
+                .rel("preload"),
+                .href(file.urlPath(for: .woff2)),
+                .as(.font),
+                .custom(
+                    name: "type",
+                    value: AssetExtension.woff2.contentType
+                ),
+                .crossorigin(.anonymous)
+            )
+        }
         link(
             .rel(.icon),
             .href(StaticFile.favicon.urlPath(