fix(property/value): icon-row hook crash when picker opens

icon-row was modified earlier in this branch (c85e8e5588) to add
< rum/reactive db-mixins/query mixins so a model/sub-block call could
refresh the entity reactively. Those mixins turn rum/defc into a class
component, but the component still called hooks/use-effect! — which
internally calls React.useEffect and is only valid inside a function
component's body. The result: an Invalid-hook-call exception every time
icon-row rendered, surfacing as a "Something wrong, please try again"
toast when the user clicked to add a page icon.

Convert rum/defc → rum/defcs (class component, takes state as first
arg) and replace the hooks/use-effect! cleanup with a :will-unmount
lifecycle. The original effect returned a cleanup that restored the
cursor when `editing?` was true on unmount; lifecycle-based unmount is
the natural equivalent.

Verified live: page reloads, picker can render icon-row without
throwing — zero hook errors in console.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/main/frontend/components/property/value.cljs

@@ -96,13 +96,16 @@
     (or (> (count selected-blocks) 1)
         (seq view-selected-blocks))))
 
-(rum/defc icon-row < rum/reactive db-mixins/query
-  [block editing?]
-  (hooks/use-effect!
-   (fn []
-     (fn []
-       (when editing?
-         (editor-handler/restore-last-saved-cursor!)))))
+(rum/defcs icon-row < rum/reactive db-mixins/query
+  {:will-unmount (fn [state]
+                   ;; The class mixins (rum/reactive + db-mixins/query) make
+                   ;; this a class component, so hooks/use-effect! is invalid
+                   ;; here. Restore the cursor on unmount via lifecycle instead.
+                   (let [[_ editing?] (:rum/args state)]
+                     (when editing?
+                       (editor-handler/restore-last-saved-cursor!)))
+                   state)}
+  [_state block editing?]
   ;; Subscribe to a fresh entity reference. Without `model/sub-block`, the
   ;; `block` prop is a stale snapshot — in-picker writes (e.g. shape changes
   ;; from the customize band) update the entity but the snapshot held by this