Adds attribute reference case to the 'of' branch in emit-set:
(set @bar of #div2 to "foo") now compiles to (dom-set-attr target "bar" "foo")
instead of falling through to the broken (set! (host-get ...)) catchall.
417/831 (50.2%), +2 from attr-of fix.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>