Rewrite the Debian installation article

app/app.config.ts

@@ -64,6 +64,11 @@ export default defineAppConfig({
         'directory tree': 'i-lucide-folder-tree',
         'ini': 'i-lucide-settings',
         'conf': 'i-lucide-settings',
+        'service': 'i-lucide-settings',
+        // Used as ::code-group tab labels when a command differs per OS.
+        'macos': 'i-simple-icons-apple',
+        'linux': 'i-simple-icons-linux',
+        'windows': 'i-simple-icons-windows',
       },
       pre: {
         slots: {

app/app.css

@@ -26,3 +26,12 @@
   }
 }
 
+/* A screenshot inside a list item (the step-by-step install guides) is
+   rendered as a bare <img> child of the <li> and gets no margin at all, so it
+   ends up glued to the text above and below it. The same image in a paragraph
+   is wrapped in a <p> that carries the prose spacing. Give it that spacing
+   back so illustrated steps stay readable. */
+li > img {
+  margin-block: 1.25rem;
+}
+