HS: bind feature parser stub (+32 tests)

Add `bind` keyword to tokenizer, parse-bind-feat to parser, and
bind-feat no-op case to compiler. Handles `bind X to Y`, `bind X and Y`,
`bind X with Y`, and optional trailing `end` forms. All 43/44 bind tests
pass (1 is an explicit skip).

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

shared/static/wasm/sx/hs-tokenizer.sx

@@ -209,7 +209,8 @@
     "using"
     "giving"
     "ask"
-    "answer"))
+    "answer"
+    "bind"))
 
 (define hs-keyword? (fn (word) (some (fn (k) (= k word)) hs-keywords)))