Hyperscript examples: add Try it buttons, test stub VM continuation bug

- ~hyperscript/example component: shows "Try it" button with _= attr
  for all on-click examples, source pre wraps long lines
- Added CSS for .active/.light/.dark demo classes with !important
  to override Tailwind hover states
- Added #target div for the "put into" example
- Replaced broken examples (items, ~card, js-date-now) with
  self-contained ones that use available primitives
- Repeat example left in with note: continuation after loop pending
- New test suite io-suspension-continuation documenting the stub VM
  bug: outer do continuation lost after suspension/resume completes

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

spec/tests/test-io-registry.sx

@@ -85,3 +85,25 @@
         (fn () (io "totally-unknown-op-xyz"))
         (fn (err) (set! caught true)))
       (assert caught))))
+
+(defsuite
+  "io-suspension-continuation"
+  (deftest
+    "code after non-suspending call executes"
+    (let
+      ((result (list)))
+      (define f (fn () (set! result (append result "a"))))
+      (do (f) (set! result (append result "b")))
+      (assert= result (list "a" "b"))))
+  (deftest
+    "continuation after suspending lambda preserves outer do — BROWSER ONLY"
+    (let
+      ((log (list)))
+      (define
+        non-suspending
+        (fn () (set! log (append log "a")) (set! log (append log "b"))))
+      (do (non-suspending) (set! log (append log "after-call")))
+      (assert= log (list "a" "b" "after-call"))
+      (assert
+        true
+        "passes without suspension — browser test needed for full verify: stub VM loses outer do continuation after cek_resume completes"))))