Fix island reactivity: trampoline callLambda result in dom-on handlers

dom-on wraps Lambda event handlers in JS functions that call callLambda.
callLambda returns a Thunk (TCO), but the wrapper never trampolined it,
so the handler body (swap!, set!, etc.) never executed. Buttons rendered
but clicks had no effect.

Fix: wrap callLambda result in trampoline() so thunks resolve and
side effects (signal mutations, DOM updates) execute.

Also use call-lambda instead of direct invocation for Lambda objects
(Lambda is a plain JS object, not callable as a function).

All 100 Playwright tests pass:
- 6 isomorphic SSR
- 5 reactive navigation (cross-demo)
- 61 geography page loads
- 7 handler response rendering
- 21 demo interaction + health checks

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/adapter-dom.sx

@@ -14,6 +14,24 @@
 (define MATH_NS "http://www.w3.org/1998/Math/MathML")
 
 
+;; --------------------------------------------------------------------------
+;; dom-on — dom-listen with post-render hooks
+;;
+;; Wraps dom-listen so that run-post-render-hooks fires after every SX
+;; event handler invocation. This is the SX-level hook integration;
+;; the native dom-listen primitive is a clean addEventListener wrapper.
+;; --------------------------------------------------------------------------
+
+(define dom-on :effects [io]
+  (fn (el name handler)
+    (dom-listen el name
+      (if (lambda? handler)
+        (if (= 0 (len (lambda-params handler)))
+          (fn () (trampoline (call-lambda handler (list))) (run-post-render-hooks))
+          (fn (e) (trampoline (call-lambda handler (list e))) (run-post-render-hooks)))
+        handler))))
+
+
 ;; --------------------------------------------------------------------------
 ;; render-to-dom — main entry point
 ;; --------------------------------------------------------------------------
@@ -199,7 +217,7 @@
                     (starts-with? attr-name "on-")
                       (let ((attr-val (trampoline (eval-expr attr-expr env))))
                         (when (callable? attr-val)
-                          (dom-listen el (slice attr-name 3) attr-val)))
+                          (dom-on el (slice attr-name 3) attr-val)))
                     ;; Two-way input binding: :bind signal
                     (= attr-name "bind")
                       (let ((attr-val (trampoline (eval-expr attr-expr env))))
@@ -1100,7 +1118,7 @@
             (when (!= (dom-get-prop el "value") v)
               (dom-set-prop el "value" v))))))
       ;; Element → signal (event listener)
-      (dom-listen el (if is-checkbox "change" "input")
+      (dom-on el (if is-checkbox "change" "input")
         (fn (e)
           (if is-checkbox
             (reset! sig (dom-get-prop el "checked"))