URL restructure, 404 page, trailing slash normalization, layout fixes

- Rename /reactive-islands/ → /reactive/, /reference/ → /hypermedia/reference/,
  /examples/ → /hypermedia/examples/ across all .sx and .py files
- Add 404 error page (not-found.sx) working on both server refresh and
  client-side SX navigation via orchestration.sx error response handling
- Add trailing slash redirect (GET only, excludes /api/, /static/, /internal/)
- Remove blue sky-500 header bar from SX docs layout (conditional on header-rows)
- Fix 405 on API endpoints from trailing slash redirect hitting POST/PUT/DELETE
- Fix client-side 404: orchestration.sx now swaps error response content
  instead of silently dropping it
- Add new plan files and home page component

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

sx/sxc/pages/docs.sx

@@ -43,18 +43,24 @@
 ;; Reference section
 ;; ---------------------------------------------------------------------------
 
-(defpage reference-index
-  :path "/reference/"
+(defpage hypermedia-index
+  :path "/hypermedia/"
   :auth :public
   :layout :sx-docs
-  :content (~sx-doc :path "/reference/" (~reference-index-content)))
+  :content (~sx-doc :path "/hypermedia/"))
+
+(defpage reference-index
+  :path "/hypermedia/reference/"
+  :auth :public
+  :layout :sx-docs
+  :content (~sx-doc :path "/hypermedia/reference/" (~reference-index-content)))
 
 (defpage reference-page
-  :path "/reference/<slug>"
+  :path "/hypermedia/reference/<slug>"
   :auth :public
   :layout :sx-docs
   :data (reference-data slug)
-  :content (~sx-doc :path (str "/reference/" slug)
+  :content (~sx-doc :path (str "/hypermedia/reference/" slug)
     (case slug
       "attributes" (~reference-attrs-content
         :req-table (~doc-attr-table-from-data :title "Request Attributes" :attrs req-attrs)
@@ -77,11 +83,11 @@
         :uniq-table (~doc-attr-table-from-data :title "Unique to sx" :attrs uniq-attrs)))))
 
 (defpage reference-attr-detail
-  :path "/reference/attributes/<slug>"
+  :path "/hypermedia/reference/attributes/<slug>"
   :auth :public
   :layout :sx-docs
   :data (attr-detail-data slug)
-  :content (~sx-doc :path "/reference/attributes"
+  :content (~sx-doc :path "/hypermedia/reference/attributes"
     (if attr-not-found
       (~reference-attr-not-found :slug slug)
       (~reference-attr-detail-content
@@ -93,11 +99,11 @@
         :wire-placeholder-id attr-wire-id))))
 
 (defpage reference-header-detail
-  :path "/reference/headers/<slug>"
+  :path "/hypermedia/reference/headers/<slug>"
   :auth :public
   :layout :sx-docs
   :data (header-detail-data slug)
-  :content (~sx-doc :path "/reference/headers"
+  :content (~sx-doc :path "/hypermedia/reference/headers"
     (if header-not-found
       (~reference-attr-not-found :slug slug)
       (~reference-header-detail-content
@@ -108,11 +114,11 @@
         :demo header-demo))))
 
 (defpage reference-event-detail
-  :path "/reference/events/<slug>"
+  :path "/hypermedia/reference/events/<slug>"
   :auth :public
   :layout :sx-docs
   :data (event-detail-data slug)
-  :content (~sx-doc :path "/reference/events"
+  :content (~sx-doc :path "/hypermedia/reference/events"
     (if event-not-found
       (~reference-attr-not-found :slug slug)
       (~reference-event-detail-content
@@ -150,16 +156,16 @@
 ;; ---------------------------------------------------------------------------
 
 (defpage examples-index
-  :path "/examples/"
+  :path "/hypermedia/examples/"
   :auth :public
   :layout :sx-docs
-  :content (~sx-doc :path "/examples/"))
+  :content (~sx-doc :path "/hypermedia/examples/"))
 
 (defpage examples-page
-  :path "/examples/<slug>"
+  :path "/hypermedia/examples/<slug>"
   :auth :public
   :layout :sx-docs
-  :content (~sx-doc :path (str "/examples/" slug)
+  :content (~sx-doc :path (str "/hypermedia/examples/" slug)
     (case slug
       "click-to-load" (~example-click-to-load)
       "form-submission" (~example-form-submission)
@@ -519,6 +525,8 @@
       "sx-proxy" (~plan-sx-proxy-content)
       "async-eval-convergence" (~plan-async-eval-convergence-content)
       "wasm-bytecode-vm" (~plan-wasm-bytecode-vm-content)
+      "generative-sx" (~plan-generative-sx-content)
+      "art-dag-sx" (~plan-art-dag-sx-content)
       :else (~plans-index-content))))
 
 ;; ---------------------------------------------------------------------------
@@ -526,16 +534,16 @@
 ;; ---------------------------------------------------------------------------
 
 (defpage reactive-islands-index
-  :path "/reactive-islands/"
+  :path "/reactive/"
   :auth :public
   :layout :sx-docs
-  :content (~sx-doc :path "/reactive-islands/" (~reactive-islands-index-content)))
+  :content (~sx-doc :path "/reactive/" (~reactive-islands-index-content)))
 
 (defpage reactive-islands-page
-  :path "/reactive-islands/<slug>"
+  :path "/reactive/<slug>"
   :auth :public
   :layout :sx-docs
-  :content (~sx-doc :path (str "/reactive-islands/" slug)
+  :content (~sx-doc :path (str "/reactive/" slug)
     (case slug
       "demo" (~reactive-islands-demo-content)
       "event-bridge" (~reactive-islands-event-bridge-content)