fix: Remove unused cookie helper functions and fix desktop sidebar visibility

1. Removed unused getPreferenceCookie and setPreferenceCookie functions
   - These were flagged by golangci-lint as unused
   - Cookie preferences now handled client-side via localStorage
   - Removed unused net/http import

2. Fixed desktop sidebar accordion auto-opening
   - Updated handleLandscapeAccordions() to open accordions in desktop view (≥769px)
   - Sidebars now show content in desktop, landscape mobile, and portrait mobile
   - Only keep accordions collapsed in portrait mobile for space saving

3. Created comprehensive multi-viewport test (66-comprehensive-all-viewports-test.mjs)
   - Tests desktop (1278px), portrait mobile (375×667), landscape mobile (667×375)
   - Validates sidebars, accordion state, content visibility, AND all buttons
   - Checks button backdrop visibility in mobile views
   - Every feature now has corresponding test coverage

Fixes golangci-lint errors:
- internal/handlers/cv_helpers.go:366: func getPreferenceCookie is unused
- internal/handlers/cv_helpers.go:375: func setPreferenceCookie is unused
- internal/handlers/cv_helpers.go:7: net/http imported and not used

internal/handlers/cv_helpers.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"log"
-	"net/http"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -361,25 +360,5 @@ func (h *CVHandler) prepareTemplateData(lang string) (map[string]interface{}, er
 // ==============================================================================
 // COOKIE HELPERS
 // ==============================================================================
-
-// getPreferenceCookie gets a preference cookie value, returns default if not found
-func getPreferenceCookie(r *http.Request, name string, defaultValue string) string {
-	cookie, err := r.Cookie(name)
-	if err != nil {
-		return defaultValue
-	}
-	return cookie.Value
-}
-
-// setPreferenceCookie sets a preference cookie (1 year expiry)
-func setPreferenceCookie(w http.ResponseWriter, name string, value string) {
-	http.SetCookie(w, &http.Cookie{
-		Name:     name,
-		Value:    value,
-		Path:     "/",
-		MaxAge:   365 * 24 * 60 * 60, // 1 year
-		HttpOnly: true,
-		SameSite: http.SameSiteStrictMode,
-		Secure:   false, // Set to true in production with HTTPS
-	})
-}
+// Note: Cookie preference management is now handled client-side via JavaScript
+// and localStorage. Server-side cookie helpers have been removed as unused.