fix: add root path redirect - EMERGENCY

The request reached the end of the pipeline - critical fix.

Added root path mapping to redirect to /taxbaik/
This ensures the root endpoint is handled.

Emergency deployment to fix production 500 error.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/TaxBaik.Web/Program.cs

@@ -395,6 +395,9 @@ app.MapHealthChecks("/healthz");
 app.MapRazorPages();  // Sitemap.cshtml, Rss.cshtml, Feed.cshtml
 app.MapStaticAssets();
 
+// 루트 경로 기본값
+app.MapGet("/", () => Results.Redirect("/taxbaik/"));
+
 // SPA 라우팅 폴백 (가장 마지막에!)
 app.MapFallbackToFile("admin/{*path:nonfile}", "admin/index.html");
 app.MapFallbackToFile("portal/{*path:nonfile}", "portal/index.html");