HS: collectionExpressions +4 (then on click, undefined where, component template)

- parser: nil return in parse-cmd for feature keywords (on/init/def/behavior/live)
  so "then on click" correctly hands off to outer coll-feats loop
- compiler: cek-try wrap for undefined variable refs in coll-where compilation
  so "doesNotExist where it > 1" returns nil instead of throwing
- integration: hs-activate! detects script[type=text/hyperscript-template] and
  applies handler to DOM instances via hs-query-all(component attr) not to script el

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/hyperscript/parser.sx

@@ -2783,6 +2783,8 @@
                       ((body (parse-cmd-list)))
                       (match-kw "end")
                       (list (quote view-transition!) using body)))))
+              ((and (= typ "keyword") (or (= val "on") (= val "init") (= val "def") (= val "behavior") (= val "live")))
+                nil)
               (true (parse-expr))))))
       (define
         parse-cmd-list