♻️ Use shared singleton containers for React portals (#8957)

Refactor use-portal-container to allocate one persistent <div> per
logical category (:modal, :popup, :tooltip, :default) instead of
creating a new div for every component instance. This keeps the DOM
clean with at most four fixed portal containers and eliminates the
arbitrary growth of empty <div> elements on document.body while
preserving the removeChild race condition fix.

frontend/src/app/main/ui/ds/tooltip/tooltip.cljs

@@ -160,7 +160,7 @@
 
         tooltip-ref (mf/use-ref nil)
 
-        container (hooks/use-portal-container)
+        container (hooks/use-portal-container :tooltip)
 
         id
         (d/nilv id internal-id)

frontend/src/app/main/ui/hooks.cljs

@@ -380,17 +380,35 @@
 
     state))
 
+(defn- get-or-create-portal-container
+  "Returns the singleton container div for the given category, creating
+  and appending it to document.body on first access."
+  [category]
+  (let [body (dom/get-body)
+        id   (str "portal-container-" category)]
+    (or (dom/query body (str "#" id))
+        (let [container (dom/create-element "div")]
+          (dom/set-attribute! container "id" id)
+          (dom/append-child! body container)
+          container))))
+
 (defn use-portal-container
-  "Creates a dedicated div container for React portals. The container
-  is appended to document.body on mount and removed on cleanup, preventing
-  removeChild race conditions when multiple portals target the same body."
-  []
-  (let [container (mf/use-memo #(dom/create-element "div"))]
-    (mf/with-effect []
-      (let [body (dom/get-body)]
-        (dom/append-child! body container)
-        #(dom/remove-child! body container)))
-    container))
+  "Returns a shared singleton container div for React portals, identified
+  by a logical category. Available categories:
+
+    :modal    — modal dialogs
+    :popup    — popups, dropdowns, context menus
+    :tooltip  — tooltips
+    :default  — general portal use (default)
+
+  All portals in the same category share one <div> on document.body,
+  keeping the DOM clean and avoiding removeChild race conditions."
+  ([]
+   (use-portal-container :default))
+  ([category]
+   (let [category (name category)]
+     (mf/with-memo [category]
+       (get-or-create-portal-container category)))))
 
 (defn use-dynamic-grid-item-width
   ([] (use-dynamic-grid-item-width nil))

frontend/src/app/main/ui/modal.cljs

@@ -84,7 +84,7 @@
 (mf/defc modal-container*
   {::mf/props :obj}
   []
-  (let [container (hooks/use-portal-container)]
+  (let [container (hooks/use-portal-container :modal)]
     (when-let [modal (mf/deref ref:modal)]
       (mf/portal
        (mf/html [:> modal-wrapper* {:data modal :key (dm/str (:id modal))}])

frontend/src/app/main/ui/workspace/tokens/management/context_menu.cljs

@@ -517,7 +517,7 @@
         dropdown-direction-change* (mf/use-ref 0)
         top                 (+ (get-in mdata [:position :y]) 5)
         left                (+ (get-in mdata [:position :x]) 5)
-        container           (hooks/use-portal-container)]
+        container           (hooks/use-portal-container :popup)]
 
     (mf/use-effect
      (mf/deps is-open?)

frontend/src/app/main/ui/workspace/tokens/management/node_context_menu.cljs

@@ -36,7 +36,7 @@
         dropdown-direction-change* (mf/use-ref 0)
         top                 (+ (get-in mdata [:position :y]) 5)
         left                (+ (get-in mdata [:position :x]) 5)
-        container           (hooks/use-portal-container)
+        container           (hooks/use-portal-container :popup)
 
         delete-node          (mf/use-fn
                               (mf/deps mdata)

frontend/src/app/main/ui/workspace/tokens/themes/theme_selector.cljs

@@ -114,7 +114,7 @@
                         :is-open? true
                         :rect rect))))))
 
-        container (hooks/use-portal-container)]
+        container (hooks/use-portal-container :popup)]
 
     [:div {:on-click on-open-dropdown
            :disabled (not can-edit?)