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>

lib/text-layout.sx

@@ -34,6 +34,21 @@
     typeset
     typeset-plain)
   (begin
+    (define
+      sublist
+      (fn
+        (lst start end)
+        (let
+          loop
+          ((i 0) (src lst) (acc (list)))
+          (cond
+            (>= i end)
+            (reverse acc)
+            (empty? src)
+            (reverse acc)
+            (>= i start)
+            (loop (+ i 1) (rest src) (cons (first src) acc))
+            :else (loop (+ i 1) (rest src) acc)))))
     (define
       measure-text
       (fn
@@ -188,8 +203,8 @@
                 (end (nth range 1))
                 (y (+ y0 (* line-idx line-height))))
               (let
-                ((line-words (slice words start end))
-                  (line-widths (slice widths start end)))
+                ((line-words (sublist words start end))
+                  (line-widths (sublist widths start end)))
                 (position-line line-words line-widths space-width x0 y))))
           line-ranges)))
     (define
@@ -221,10 +236,10 @@
                 (let
                   ((start (first range)) (end (nth range 1)))
                   (let
-                    ((lw (slice words start end))
-                      (lwid (slice widths start end)))
+                    ((lw (sublist words start end))
+                      (lwid (sublist widths start end)))
                     (let
-                      ((total-w (reduce + 0 lwid))
+                      ((total-w (let sum-loop ((k 0) (t 0)) (if (>= k (len lwid)) t (sum-loop (+ k 1) (+ t (nth lwid k))))))
                         (n-gaps (max 1 (- (len lw) 1)))
                         (is-last (= line-idx (- n-lines 1))))
                       (let