Reactive island preservation across server-driven morphs

Islands survive hypermedia swaps: morph-node skips hydrated
data-sx-island elements when the same island exists in new content.
dispose-islands-in skips hydrated islands to prevent premature cleanup.

- @client directive: .sx files marked ;; @client send define forms to browser
- CSSX client-side: cssxgroup renamed (no hyphen) to avoid isRenderExpr
  matching it as a custom element — was producing [object HTMLElement]
- Island wrappers: div→span to avoid block-in-inline HTML parse breakage
- ~sx-header is now a defisland with inline reactive colour cycling
- bootstrap_js.py defaults output to shared/static/scripts/sx-browser.js
- Deleted stale sx-ref.js (sx-browser.js is the canonical browser build)
- Hegelian Synthesis essay: dialectic of hypertext and reactivity
- component-source helper handles Island types for docs pretty-printing

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

sx/sxc/pages/docs.sx

@@ -221,6 +221,7 @@
       "no-alternative" (~essay-no-alternative)
       "zero-tooling" (~essay-zero-tooling)
       "react-is-hypermedia" (~essay-react-is-hypermedia)
+      "hegelian-synthesis" (~essay-hegelian-synthesis)
       :else (~essays-index-content))))
 
 ;; ---------------------------------------------------------------------------
@@ -516,6 +517,8 @@
       "sx-forge" (~plan-sx-forge-content)
       "sx-swarm" (~plan-sx-swarm-content)
       "sx-proxy" (~plan-sx-proxy-content)
+      "async-eval-convergence" (~plan-async-eval-convergence-content)
+      "wasm-bytecode-vm" (~plan-wasm-bytecode-vm-content)
       :else (~plans-index-content))))
 
 ;; ---------------------------------------------------------------------------