Playwright sandbox: offline browser test environment for WASM kernel

New sx_playwright mode="sandbox" — injects the WASM kernel into about:blank
with full FFI, IO suspension tracing, and real DOM. No server needed.

Predefined stacks: core (kernel only), web (full web stack), hs (+ hyperscript),
test (+ test framework). Custom files and setup expressions supported.

Reproduces the host-callback IO suspension bug: direct callFn chains 6/6
suspensions correctly, but host-callback → addEventListener → _driveAsync
only completes 1/6. Bug is in the _driveAsync resume chain context.

Also: debug.sx mock DOM harness, test_hs_repeat.js Node.js reproduction.

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

lib/hyperscript/tokenizer.sx

@@ -152,7 +152,8 @@
     "includes"
     "contain"
     "undefined"
-    "exist"))
+    "exist"
+    "match"))
 
 (define hs-keyword? (fn (word) (some (fn (k) (= k word)) hs-keywords)))