HS toggle style: parse between/cycle, runtime, mock style dict

Parser:
- Reorder toggle style parsing: target before between clause
- Handle "indexed" keyword, "indexed by" syntax
- Use parse-atom (not parse-expr) for between values to avoid
  consuming "and" as boolean operator
- Support 3-4 value cycles via toggle-style-cycle

Compiler:
- Add toggle-style-cycle dispatch → hs-toggle-style-cycle!

Runtime:
- Add hs-toggle-style-between! (2-value toggle)
- Add hs-toggle-style-cycle! (N-value round-robin)

Mock DOM:
- Parse CSS strings from setAttribute "style" into style sub-dict
  so dom-get-style/dom-set-style work correctly

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

lib/hyperscript/compiler.sx

@@ -1008,6 +1008,14 @@
                   (nth ast 1)
                   (hs-to-sx (nth ast 2))
                   (hs-to-sx (nth ast 3))))
+              ((= head (quote toggle-style-cycle))
+                (list
+                  (quote hs-toggle-style-cycle!)
+                  (hs-to-sx (nth ast 2))
+                  (nth ast 1)
+                  (cons
+                    (quote list)
+                    (map hs-to-sx (slice ast 3 (len ast))))))
               ((= head (quote toggle-attr))
                 (list
                   (quote hs-toggle-attr!)