Fix browser compat: sublist replaces 3-arg slice, manual sum replaces reduce

- Added sublist helper (portable list extraction, avoids 3-arg slice
  which fails in browser WASM kernel)
- Replaced reduce + 0 lwid with manual sum loop (reduce has browser
  compat issues with dict-set! error in call stack)
- Imperative DOM update via effect for clean paragraph re-rendering
  on signal changes (clear container, create new spans)
- String slice in hyphenate-word kept (works on strings)

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

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

@@ -1553,18 +1553,20 @@
             cl-collect
             (fn
               (acc)
-              (let
-                ((cmd (parse-cmd)))
-                (if
-                  (nil? cmd)
-                  acc
-                  (let
-                    ((acc2 (append acc (list cmd))))
-                    (cond
-                      ((match-kw "then") (cl-collect acc2))
-                      ((and (not (at-end?)) (= (tp-type) "keyword") (cmd-kw? (tp-val)))
-                        (cl-collect acc2))
-                      (true acc2)))))))
+              (do
+                (match-kw "then")
+                (let
+                  ((cmd (parse-cmd)))
+                  (if
+                    (nil? cmd)
+                    acc
+                    (let
+                      ((acc2 (append acc (list cmd))))
+                      (cond
+                        ((match-kw "then") (cl-collect acc2))
+                        ((and (not (at-end?)) (= (tp-type) "keyword") (cmd-kw? (tp-val)))
+                          (cl-collect acc2))
+                        (true acc2))))))))
           (let
             ((cmds (cl-collect (list))))
             (cond