fix :infer-warning on isSymbolNode property access in parse-variables

Add ^js type hint so the ClojureScript compiler knows the element is a
plain JS object and stops attempting type inference on the property.

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

frontend/src/cljs/microtables_frontend/utils/data.cljs

@@ -27,7 +27,7 @@
 
 (def parse-variables (memoize (fn [expression]
                                 (as-> (js->clj (.parse mathjs (replace-ranges-in-expression expression))) $
-                                  (.filter $ #(true? (.-isSymbolNode %)))
+                                  (.filter $ #(true? (.-isSymbolNode ^js %)))
                                   (map #(.-name %) $)
                                   (map #(.toUpperCase %) $)
                                   (filter #(re-matches #"[A-Z]+[0-9]+" %) $)))))