Record robots.txt/sitemap.xml GETs, emoji-mark machinery steps in trails

The robots and sitemap routes never called _record_get, so those
accesses were invisible. Recorded like page GETs, they surface as
crawler hits at display time (no activity message ever follows). In
the trail rendering, known non-article machinery paths (robots,
sitemap, future feed paths) get an emoji marker instead of a bare
slug.

frontend/src/analytics/format.js

@@ -160,9 +160,30 @@ function externalOrigin(url) {
   }
 }
 
+// Non-article machinery paths shown in trails with an emoji marker:
+// recorded like page GETs but fetched by crawlers/feed readers, so they
+// surface in the crawler rows. Feed paths are pre-registered for the
+// future RSS/Atom routes.
+const MACHINE_STEPS = {
+  '/robots.txt': ['🤖', 'robots.txt'],
+  '/sitemap.xml': ['🗺️', 'sitemap.xml'],
+  '/rss.xml': ['📡', 'rss.xml'],
+  '/atom.xml': ['📡', 'atom.xml'],
+  '/feed': ['📡', 'feed'],
+  '/feed.xml': ['📡', 'feed.xml'],
+}
+
 /** Format one trail step: an internal page or an external https origin. */
 function stepOf(path, titles) {
   if (path?.startsWith('/')) {
+    // Known non-article machinery GETs (fetched by crawlers and feed
+    // readers, recorded like page GETs): emoji-marked so they stand out
+    // from article steps in the trails.
+    const machine = MACHINE_STEPS[path]
+    if (machine) {
+      const [emoji, name] = machine
+      return { path, slug: `${emoji} ${name}`, title: name, external: false, machine: true }
+    }
     return { path, slug: slugOf(path), title: titles.get(path) || '', external: false, home: path === '/' }
   }
   if (path?.startsWith('https://')) {