Fix SX history, OOB header swaps, cross-service nav components

- Always re-fetch on popstate (drop LRU cache) for fresh content on back/forward
- Save/restore scroll position via pushState
- Add id="root-header-child" to ~app-body so OOB swaps can target it
- Fix OOB renderers: nest root-row inside root-header-child swap instead of
  separate OOB that clobbers it
- Fix 3+ header rows dropped: wrap all headers in single fragment instead of
  concatenating outside (<> ...)
- Strip <script data-components> from text/sx responses before renderToString
- Fall back to location.assign for cross-origin pushState (SecurityError)
- Move blog/sx/nav.sx to shared/sx/templates/ so all services have nav components

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

shared/sx/templates/layout.sx

@@ -6,7 +6,7 @@
           (header :class "z-50"
             (div :id "root-header-summary"
                  :class "flex items-start gap-2 p-1 bg-sky-500"
-              (div :class "flex flex-col w-full items-center"
+              (div :id "root-header-child" :class "flex flex-col w-full items-center"
                 (when header-rows header-rows)))))
         (div :id "root-menu" :sx-swap-oob "outerHTML" :class "md:hidden"
           (when menu menu))))
@@ -107,13 +107,12 @@
         (div :id child-id :class "flex flex-col w-full items-center"
           (when child child))))))
 
-(defcomp ~oob-header-sx (&key parent-id child-id row)
-  (div :id parent-id :sx-swap-oob "outerHTML" :class "w-full"
-    (div :class "w-full" row
-      (div :id child-id))))
+(defcomp ~oob-header-sx (&key parent-id row)
+  (div :id parent-id :sx-swap-oob "outerHTML" :class "flex flex-col w-full items-center"
+    row))
 
 (defcomp ~header-child-sx (&key id inner)
-  (div :id (or id "root-header-child") :class "w-full" inner))
+  (div :id (or id "root-header-child") :class "flex flex-col w-full items-center" inner))
 
 (defcomp ~error-content (&key errnum message image)
   (div :class "text-center p-8 max-w-lg mx-auto"