fix: prevent single-day streaks from being shown

A streak requires at least 2 consecutive days. Return 0 when the
count is less than 2 so the streak counter is not displayed after
completing only today's puzzle.

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

src/routes/api/streak/+server.ts

@@ -32,5 +32,5 @@ export const GET: RequestHandler = async ({ url }) => {
 		cursor.setDate(cursor.getDate() - 1);
 	}
 
-	return json({ streak });
+	return json({ streak: streak < 2 ? 0 : streak });
 };