fix: Resolve CSS bundling in production and lint errors

- Fix golangci-lint errcheck errors by using t.Setenv() instead of os.Setenv()
- Add CSS bundle build step to deploy workflow for production
- Add graceful fallback to modular CSS if bundle doesn't exist
- Remove unused os import from preferences_test.go

internal/handlers/cv_helpers.go

@@ -330,8 +330,16 @@ func (h *CVHandler) prepareTemplateData(lang string) (map[string]interface{}, er
 	// Get current year
 	currentYear := time.Now().Year()
 
-	// Check if production mode
+	// Check if production mode AND CSS bundle exists
+	// This ensures graceful fallback to modular CSS if bundle not built
 	isProduction := os.Getenv("GO_ENV") == "production"
+	if isProduction {
+		bundlePath := filepath.Join("static", "dist", "bundle.min.css")
+		if _, err := os.Stat(bundlePath); os.IsNotExist(err) {
+			// Bundle doesn't exist, fall back to modular CSS
+			isProduction = false
+		}
+	}
 
 	// Prepare template data
 	data := map[string]interface{}{