Phase 7c + 7d: optimistic data updates and offline mutation queue

7c — Optimistic Data Updates:
- orchestration.sx: optimistic-cache-update/revert/confirm + submit-mutation
- pages.py: mount_action_endpoint at /sx/action/<name> for client mutations
- optimistic-demo.sx: live demo with todo list, pending/confirmed/reverted states
- helpers.py: demo data + add-demo-item action handler

7d — Offline Data Layer:
- orchestration.sx: connectivity tracking, offline-queue-mutation, offline-sync,
  offline-aware-mutation (routes online→submit, offline→queue)
- offline-demo.sx: live demo with notes, connectivity indicator, sync timeline
- helpers.py: offline demo data

Also updates plans.sx: marks Phase 7 fully complete (all 6 sub-phases 7a-7f).

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

sx/sxc/pages/docs.sx

@@ -525,6 +525,30 @@
   :data (affinity-demo-data)
   :content (~affinity-demo-content :components components :page-plans page-plans))
 
+(defpage optimistic-demo
+  :path "/isomorphism/optimistic"
+  :auth :public
+  :layout (:sx-section
+    :section "Isomorphism"
+    :sub-label "Isomorphism"
+    :sub-href "/isomorphism/"
+    :sub-nav (~section-nav :items isomorphism-nav-items :current "Optimistic")
+    :selected "Optimistic")
+  :data (optimistic-demo-data)
+  :content (~optimistic-demo-content :items items :server-time server-time))
+
+(defpage offline-demo
+  :path "/isomorphism/offline"
+  :auth :public
+  :layout (:sx-section
+    :section "Isomorphism"
+    :sub-label "Isomorphism"
+    :sub-href "/isomorphism/"
+    :sub-nav (~section-nav :items isomorphism-nav-items :current "Offline")
+    :selected "Offline")
+  :data (offline-demo-data)
+  :content (~offline-demo-content :notes notes :server-time server-time))
+
 ;; Wildcard must come AFTER specific routes (first-match routing)
 (defpage isomorphism-page
   :path "/isomorphism/<slug>"