fix(ui): stop the add-provider modal from shifting while it loads (#13179)

ui/store/lighthouse-llm/store.ts

@@ -0,0 +1,25 @@
+import { create } from "zustand";
+
+interface LighthouseLlmStoreState {
+  // Last answer this page load (null: never checked), shown at once on reopen.
+  hasConnectedLlm: boolean | null;
+  // Id of the newest check: an older check that answers late is ignored.
+  latestCheck: number;
+  startCheck: () => number;
+  settleCheck: (check: number, hasConnectedLlm: boolean) => void;
+}
+
+export const useLighthouseLlmStore = create<LighthouseLlmStoreState>(
+  (set, get) => ({
+    hasConnectedLlm: null,
+    latestCheck: 0,
+    startCheck: () => {
+      const check = get().latestCheck + 1;
+      set({ latestCheck: check });
+      return check;
+    },
+    settleCheck: (check, hasConnectedLlm) => {
+      if (check === get().latestCheck) set({ hasConnectedLlm });
+    },
+  }),
+);