h3 v2's setCookie modifies event response headers but doesn't
carry them when handler returns a raw Response object. Build
Set-Cookie header manually in redirect helpers instead.
h3 v2's html() is a tagged template literal, not a function that
accepts a string. JSX-rendered markup passed directly causes
"first.reduce is not a function". Created htmlPage() helper that
wraps markup in a proper Response with text/html content type.
