🐛 Fix num-linked-libraries to use select-libraries instead of all files

refs/select-libraries filters to only files that are libraries
of the current file (including itself), so (dec (count libraries))
now correctly returns the number of linked external libraries.

Closes #11106

AI-assisted-by: mimo-v2.5-pro

frontend/src/app/main/data/workspace.cljs

@@ -276,7 +276,7 @@
           (compute-stats [state]
             (let [file      (dsh/lookup-file state file-id)
                   file-data (:data file)
-                  libraries (dsh/lookup-libraries state)
+                  libraries (refs/select-libraries (:files state) file-id)
                   shapes    (count-shapes-per-page file-data)
                   n-pages   (count (:pages file-data))
                   n-shapes  (reduce + 0 shapes)