Step 18 (part 3): Expand parser — expressions, commands, features

Tokenizer:
  * and % now emit as operators (were silently swallowed)
  Added keywords: install, measure, behavior, called
  5 new arithmetic operator tests

Parser — expression layer:
  Arithmetic (+, -, *, /, %) via parse-arith
  Unary not, no, unary minus
  the X of Y possessive (parse-the-expr)
  as Type conversion, X in Y membership, array literals [...]
  fetch URL parsing fixed — no longer consumes "as" meant for fetch

Parser — 8 new commands:
  return, throw, append...to, tell...end, for...in...end,
  make a Type, install Behavior, measure

Parser — 2 new features:
  def name(params)...end, behavior Name(params)...end

Parser — enhanced:
  wait for event [from target], on every event modifier

33 new parser tests (16 suites), 5 tokenizer tests.
3043/3043 full build, zero regressions.

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

lib/hyperscript/tokenizer.sx

@@ -133,7 +133,11 @@
     "than"
     "greater"
     "class"
-    "anything"))
+    "anything"
+    "install"
+    "measure"
+    "behavior"
+    "called"))
 
 (define hs-keyword? (fn (word) (some (fn (k) (= k word)) hs-keywords)))
 
@@ -507,6 +511,10 @@
                 (do (hs-emit! "op" ">" start) (hs-advance! 1) (scan!))
                 (= ch "!")
                 (do (hs-emit! "op" "!" start) (hs-advance! 1) (scan!))
+                (= ch "*")
+                (do (hs-emit! "op" "*" start) (hs-advance! 1) (scan!))
+                (= ch "%")
+                (do (hs-emit! "op" "%" start) (hs-advance! 1) (scan!))
                 (= ch ".")
                 (do (hs-emit! "dot" "." start) (hs-advance! 1) (scan!))
                 :else (do (hs-advance! 1) (scan!)))))))