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/signals.sx

@@ -133,6 +133,8 @@
 
         ;; Initial computation
         (recompute)
+        ;; Auto-register disposal with island scope
+        (register-in-scope (fn () (dispose-computed s)))
         s))))
 
 
@@ -176,13 +178,17 @@
         (run-effect)
 
         ;; Return dispose function
-        (fn ()
-          (set! disposed true)
-          (when cleanup-fn (invoke cleanup-fn))
-          (for-each
-            (fn (dep) (signal-remove-sub! dep run-effect))
-            deps)
-          (set! deps (list)))))))
+        (let ((dispose-fn
+                (fn ()
+                  (set! disposed true)
+                  (when cleanup-fn (invoke cleanup-fn))
+                  (for-each
+                    (fn (dep) (signal-remove-sub! dep run-effect))
+                    deps)
+                  (set! deps (list)))))
+          ;; Auto-register with island scope so disposal happens on swap
+          (register-in-scope dispose-fn)
+          dispose-fn)))))
 
 
 ;; --------------------------------------------------------------------------