Stabilize mobile auth session handling

app/(auth)/sign-in.tsx

@@ -19,6 +19,7 @@ import { useAppTheme } from "@/contexts/ThemeContext";
 import { fetchAuthCapabilities } from "@/lib/auth-capabilities";
 import { signInWithAuthentik } from "@/lib/auth-oauth";
 import { completeSignInAfterAuth } from "@/lib/complete-sign-in";
+import { formatAuthErrorMessage } from "@/lib/trpc-errors";
 import { isRequiredString, isValidEmail, useFieldVisibility } from "@/lib/form-validation";
 
 export default function SignInScreen() {
@@ -81,12 +82,7 @@ export default function SignInScreen() {
       });
 
       if (signInError) {
-        const message = signInError.message ?? "";
-        if (message.toLowerCase().includes("internal") || message.includes("500")) {
-          setError("Server error — is the API running with Postgres? Check beenvoice dev + docker.");
-        } else {
-          setError(message || "Invalid email or password");
-        }
+        setError(formatAuthErrorMessage(signInError));
         return;
       }
 
@@ -108,7 +104,7 @@ export default function SignInScreen() {
       );
 
       if (oauthError) {
-        setError(oauthError.message ?? "Could not sign in with Authentik");
+        setError(formatAuthErrorMessage(oauthError));
         return;
       }