fix(login): readable email-OTP send error instead of raw '{}'

gotrue can throw an error whose message is an unhelpful JSON blob (e.g. 500
'Error sending magic link email' when Supabase SMTP isn't configured). Show a
readable, actionable message instead of rendering the raw payload.

src/components/portal/login-flow.tsx

@@ -454,7 +454,14 @@ function OtpVerify({ account, email, initialChannel = "email", remember, setReme
         if (!PHONE_RE.test(phone)) { setError("Enter your phone in international format, e.g. +14155550100."); return; }
         await sendPhoneOtp(phone); setSent(true);
       }
-    } catch (e) { setError((e as Error).message); }
+    } catch (e) {
+      // gotrue can throw an error whose message is an unhelpful "{}"/JSON blob (e.g. a
+      // 500 "Error sending magic link email" when SMTP isn't set up). Show something
+      // readable and actionable instead of the raw payload.
+      const raw = (e as { message?: unknown })?.message;
+      const readable = typeof raw === "string" && raw.trim() && !raw.trim().startsWith("{") ? raw.trim() : "";
+      setError(readable || "We couldn't send your sign-in code right now. Please try again shortly, or sign in with your password.");
+    }
   }
 
   async function complete(code: string) {