Add initial speculation rules implementation.

private/apache2/directory.conf

@@ -128,3 +128,11 @@
   RewriteCond %1.%2 -f
   RewriteRule ^(.*)\.\d{14}\.(avif|css|js|png|svg|webp|woff|woff2)$ $1.${RELEASE_TIMESTAMP}.$2 [L,NE,R=permanent]
 </IfModule>
+
+<FilesMatch "speculation-rules\.json">
+  Header set Content-Type: "application/speculationrules+json"
+</FilesMatch>
+
+<FilesMatch ".*\.html$">
+   Header set Speculation-Rules: '"/speculation-rules.json"'
+</FilesMatch>

src/ssg/ValueObjects/InputFileCollection.php

@@ -49,7 +49,8 @@ public function getSitemapEntries(): array
             \assert(\is_string($slug));
 
             if (
-                'robots.txt' === $slug
+                'speculation-rules.json' === $slug
+                || 'robots.txt' === $slug
                 || 'sitemap.xml' === $slug
                 || str_starts_with($slug, 'google')
                 || str_ends_with($slug, '.atom')

src/ssg/input/speculation-rules.json

@@ -0,0 +1,18 @@
+{
+  "prefetch": [
+    {
+      "where": {
+        "selector_matches": "a[href^='/']"
+      },
+      "eagerness": "immediate"
+    }
+  ],
+  "prerender": [
+    {
+      "where": {
+        "selector_matches": "a[href^='/']"
+      },
+      "eagerness": "moderate"
+    }
+  ]
+}