Island disposal, reactive lists, input binding, and Phase 2 plan

- Effect and computed auto-register disposers with island scope via
  register-in-scope; dispose-islands-in called before every swap point
  (orchestration.sx) to clean up intervals/subscriptions on navigation.
- Map + deref inside islands auto-upgrades to reactive-list for signal-
  bound list rendering. Demo island with add/remove items.
- New :bind attribute for two-way signal-input binding (text, checkbox,
  radio, textarea, select). bind-input in adapter-dom.sx handles both
  signal→element (effect) and element→signal (event listener).
- Phase 2 plan page at /reactive-islands/phase2 covering input binding,
  keyed reconciliation, reactive class/style, refs, portals, error
  boundaries, suspense, and transitions.
- Updated status tables in overview and plan pages.
- Fixed stopwatch reset (fn body needs do wrapper for multiple exprs).

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

shared/sx/ref/boot.sx

@@ -391,6 +391,15 @@
           disposers)
         (dom-set-data el "sx-disposers" nil)))))
 
+(define dispose-islands-in
+  (fn (root)
+    ;; Dispose all islands within root before a swap replaces them.
+    (when root
+      (let ((islands (dom-query-all root "[data-sx-island]")))
+        (when (and islands (not (empty? islands)))
+          (log-info (str "disposing " (len islands) " island(s)"))
+          (for-each dispose-island islands))))))
+
 
 ;; --------------------------------------------------------------------------
 ;; Full boot sequence