🐛 Add project-id guard to use-plugin-register layout effect (#10859)

Add `project-id` to the guard condition in `use-plugin-register`'s layout effect so the plugin "Try out" flow waits until projects have loaded.

Previously, only `plugin-url` was checked, which allowed the fetch to fire
before projects were available, sending a nil `project-id` and causing a 400
validation error from the backend.

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

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

@@ -211,7 +211,7 @@
 
     (mf/with-layout-effect
       [plugin-url team-id project-id]
-      (when plugin-url
+      (when (and plugin-url project-id)
         (->> (dp/fetch-manifest plugin-url)
              (rx/subs!
               (fn [plugin]