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>

sx/sxc/pages/docs.sx

@@ -668,6 +668,7 @@
     "event-bridge" (~reactive-islands-event-bridge-content)
     "named-stores" (~reactive-islands-named-stores-content)
     "plan" (~reactive-islands-plan-content)
+    "phase2" (~reactive-islands-phase2-content)
     :else (~reactive-islands-index-content)))
 
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