diff --git a/app/ui/app.go b/app/ui/app.go
index d73df2c02..f84dd8d2e 100644
--- a/app/ui/app.go
+++ b/app/ui/app.go
@@ -7,7 +7,9 @@ import (
 	"embed"
 	"errors"
 	"io/fs"
+	"mime"
 	"net/http"
+	"path/filepath"
 	"strings"
 	"time"
 )
@@ -15,6 +17,13 @@ import (
 //go:embed app/dist
 var appFS embed.FS
 
+func init() {
+	mime.AddExtensionType(".js", "application/javascript; charset=utf-8")
+	mime.AddExtensionType(".css", "text/css; charset=utf-8")
+	mime.AddExtensionType(".woff2", "font/woff2")
+	mime.AddExtensionType(".svg", "image/svg+xml")
+}
+
 // appHandler returns an HTTP handler that serves the React SPA.
 // It tries to serve real files first, then falls back to index.html for React Router.
 func (s *Server) appHandler() http.Handler {
@@ -24,11 +33,19 @@ func (s *Server) appHandler() http.Handler {
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		p := strings.TrimPrefix(r.URL.Path, "/")
-		if _, err := fsys.Open(p); err == nil {
-			// Serve the file directly
+
+		if file, err := fsys.Open(p); err == nil {
+			file.Close()
+
+			// Ensure proper Content-Type headers
+			if contentType := mime.TypeByExtension(filepath.Ext(p)); contentType != "" {
+				w.Header().Set("Content-Type", contentType)
+			}
+
 			fileServer.ServeHTTP(w, r)
 			return
 		}
+
 		// Fallback – serve index.html for unknown paths so React Router works
 		data, err := fs.ReadFile(fsys, "index.html")
 		if err != nil {
@@ -39,6 +56,8 @@ func (s *Server) appHandler() http.Handler {
 			}
 			return
 		}
+
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 		http.ServeContent(w, r, "index.html", time.Time{}, bytes.NewReader(data))
 	})
 }
diff --git a/app/ui/app_test.go b/app/ui/app_test.go
new file mode 100644
index 000000000..fedacb3ac
--- /dev/null
+++ b/app/ui/app_test.go
@@ -0,0 +1,39 @@
+//go:build windows || darwin
+
+package ui
+
+import (
+	"io/fs"
+	"strings"
+	"testing"
+)
+
+// TestEmbeddedAssets verifies that the correct UI assets are embedded.
+// This test will FAIL THE BUILD if wrong files are embedded.
+func TestEmbeddedAssets(t *testing.T) {
+	fsys, err := fs.Sub(appFS, "app/dist")
+	if err != nil {
+		t.Fatal("app/dist not found in embedded filesystem - UI not built")
+	}
+
+	data, err := fs.ReadFile(fsys, "index.html")
+	if err != nil {
+		t.Fatal("index.html not found - run 'go generate' first")
+	}
+
+	html := string(data)
+
+	if strings.Contains(html, "/src/main.tsx") {
+		t.Fatal("Wrong index.html embedded: has /src/main.tsx (dev paths). The UI was not built. Run 'npm run build' first.")
+	}
+
+	if !strings.Contains(html, "/assets/index-") {
+		t.Fatal("Wrong index.html embedded: missing /assets/index-* (production paths). The UI was not built correctly.")
+	}
+
+	if _, err := fsys.Open("assets"); err != nil {
+		t.Fatal("assets/ directory not found - UI build incomplete")
+	}
+
+	t.Log("Embedded assets verified - UI built correctly")
+}