fix: store axios instance correctly in useState

An axios instance (returned by axios.create()) is itself a callable
function. React's useState setter treats any function argument as an
updater callback, calling it with the previous state instead of storing
it as the new value. This caused setClient(createClient(...)) to invoke
the axios instance with null, store the resulting Promise as client,
and produce "client.get is not a function (it is undefined)" at runtime.

Fix: wrap in an arrow function so React uses the instance as the return
value of the updater rather than as the updater itself.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

artifacts/postiz-mobile/context/PostizContext.tsx

@@ -94,7 +94,7 @@ export function PostizProvider({ children }: { children: React.ReactNode }) {
           const url = (storedUrl || DEFAULT_BASE_URL).replace(/\/$/, "");
           setApiKey(storedKey);
           setBaseUrl(url);
-          setClient(createClient(storedKey, url));
+          setClient(() => createClient(storedKey, url));
         }
       } catch {
       } finally {
@@ -109,7 +109,7 @@ export function PostizProvider({ children }: { children: React.ReactNode }) {
       await SecureStore.setItemAsync(BASE_URL_STORAGE, newBaseUrl);
       setApiKey(newApiKey);
       setBaseUrl(newBaseUrl);
-      setClient(createClient(newApiKey, newBaseUrl));
+      setClient(() => createClient(newApiKey, newBaseUrl));
     },
     []
   );