Gate server-side component expansion with contextvar, fix nth arg order, add GEB essay and manifesto links

- Add _expand_components contextvar so _aser only expands components
  during page slot evaluation (fixes highlight on examples, avoids
  breaking fragment responses)
- Fix nth arg order (nth coll n) in docs.sx, examples.sx (delete-row,
  edit-row, bulk-update)
- Add "Godel, Escher, Bach and SX" essay with Wikipedia links
- Update SX Manifesto: new authors, Wikipedia links throughout,
  remove Marx/Engels link

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sxc/docs.sx

@@ -61,15 +61,15 @@
 (defcomp ~doc-nav (&key items current)
   (nav :class "flex flex-wrap gap-2 mb-8"
     (map (fn (item)
-      (a :href (nth 1 item)
-         :sx-get (nth 1 item)
+      (a :href (nth item 1)
+         :sx-get (nth item 1)
          :sx-target "#main-panel"
          :sx-select "#main-panel"
          :sx-swap "outerHTML"
          :sx-push-url "true"
          :class (str "px-3 py-1.5 rounded text-sm font-medium no-underline "
-                     (if (= (nth 0 item) current)
+                     (if (= (nth item 0) current)
                        "bg-violet-100 text-violet-800"
                        "bg-stone-100 text-stone-600 hover:bg-stone-200"))
-        (nth 0 item)))
+        (nth item 0)))
       items)))