Fix standalone OOB layout: delegate to shared layout for proper OOB swaps

The standalone OOB layout was returning nil, so SPA navigation
responses had no OOB swap structure. The header island wasn't
included in responses, so:
- Colour state was lost (island not morphed, signals reset)
- Copyright path wasn't updated (lake not in response)

Now delegates to ~shared:layout/oob-sx which wraps content in
proper OOB sections (filter, aside, menu, main-panel). The header
island with updated :path is included in the content, allowing
the morph to preserve island signals and update lakes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sx/sx/layouts.sx

@@ -168,9 +168,10 @@
 (defcomp ~layouts/standalone-docs-layout-full ()
   nil)
 
-;; Standalone OOB: nothing needed — nav is in content.
-(defcomp ~layouts/standalone-docs-layout-oob ()
-  nil)
+;; Standalone OOB: delegate to shared layout for proper OOB swap structure.
+;; The content (with nav + header island) goes into #main-panel via sx-swap-oob.
+(defcomp ~layouts/standalone-docs-layout-oob (&key content) :affinity :server
+  (~shared:layout/oob-sx :content content))
 
 ;; Standalone mobile: nothing — nav is in content.
 (defcomp ~layouts/standalone-docs-layout-mobile ()