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/examples.sx

@@ -91,7 +91,7 @@
           (th :class "px-3 py-2 font-medium text-stone-600 w-20" "")))
       (tbody :id "delete-rows"
         (map (fn (item)
-          (~delete-row :id (nth 0 item) :name (nth 1 item)))
+          (~delete-row :id (nth item 0) :name (nth item 1)))
           items)))))
 
 (defcomp ~delete-row (&key id name)
@@ -344,7 +344,7 @@
           (th :class "px-3 py-2 font-medium text-stone-600 w-24" "")))
       (tbody :id "edit-rows"
         (map (fn (row)
-          (~edit-row-view :id (nth 0 row) :name (nth 1 row) :price (nth 2 row) :stock (nth 3 row)))
+          (~edit-row-view :id (nth row 0) :name (nth row 1) :price (nth row 2) :stock (nth row 3)))
           rows)))))
 
 (defcomp ~edit-row-view (&key id name price stock)
@@ -415,7 +415,7 @@
             (th :class "px-3 py-2 font-medium text-stone-600" "Status")))
         (tbody :id "bulk-table"
           (map (fn (u)
-            (~bulk-row :id (nth 0 u) :name (nth 1 u) :email (nth 2 u) :status (nth 3 u)))
+            (~bulk-row :id (nth u 0) :name (nth u 1) :email (nth u 2) :status (nth u 3)))
             users))))))
 
 (defcomp ~bulk-row (&key id name email status)