Add missing plan routes for cek-reactive and reactive-runtime

Both plans had nav entries and component files but were missing from
the page-functions.sx case statement, causing 404s on their URLs.

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

sx/sx/page-functions.sx

@@ -535,4 +535,6 @@
         "sx-protocol" '(~plans/sx-protocol/plan-sx-protocol-content)
         "scoped-effects" '(~plans/scoped-effects/plan-scoped-effects-content)
         "foundations" '(~plans/foundations/plan-foundations-content)
+        "cek-reactive" '(~plans/cek-reactive/plan-cek-reactive-content)
+        "reactive-runtime" '(~plans/reactive-runtime/plan-reactive-runtime-content)
         :else '(~plans/index/plans-index-content)))))

sx/sxc/pages/docs.sx

@@ -579,6 +579,7 @@
       "scoped-effects" (~plans/scoped-effects/plan-scoped-effects-content)
       "foundations" (~plans/foundations/plan-foundations-content)
       "cek-reactive" (~plans/cek-reactive/plan-cek-reactive-content)
+      "reactive-runtime" (~plans/reactive-runtime/plan-reactive-runtime-content)
       :else (~plans/index/plans-index-content))))
 
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