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>

shared/sx/ref/adapter-html.sx

@@ -349,13 +349,13 @@
         (let ((body-html (render-to-html (component-body island) local))
               (state-json (serialize-island-state kwargs)))
           ;; Wrap in container with hydration attributes
-          (str "<div data-sx-island=\"" (escape-attr island-name) "\""
+          (str "<span data-sx-island=\"" (escape-attr island-name) "\""
                (if state-json
                  (str " data-sx-state=\"" (escape-attr state-json) "\"")
                  "")
                ">"
                body-html
-               "</div>"))))))
+               "</span>"))))))
 
 
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