Add impersonate banner (#14734)

Related to https://github.com/twentyhq/twenty/pull/14360

<img width="1511" height="468" alt="Screenshot 2025-09-26 at 12 16 46"
src="https://github.com/user-attachments/assets/33e0e0b5-1226-455d-90f2-e4fc3deef7a8"
/>

@Bonapara, let you tell me if wording and banner color are ok. This
banner is displayed when a user is impersonating an other user

packages/twenty-front/src/modules/auth/states/isImpersonatingState.ts

@@ -0,0 +1,24 @@
+import { jwtDecode } from 'jwt-decode';
+import { selector } from 'recoil';
+import { isDefined } from 'twenty-shared/utils';
+import { tokenPairState } from './tokenPairState';
+
+export const isImpersonatingState = selector<boolean>({
+  key: 'isImpersonatingState',
+  get: ({ get }) => {
+    const tokenPair = get(tokenPairState);
+
+    if (!isDefined(tokenPair?.accessOrWorkspaceAgnosticToken?.token)) {
+      return false;
+    }
+
+    try {
+      const decodedToken = jwtDecode<{ isImpersonating: boolean }>(
+        tokenPair.accessOrWorkspaceAgnosticToken.token,
+      );
+      return decodedToken?.isImpersonating ?? false;
+    } catch {
+      return false;
+    }
+  },
+});